EXHIBIT 10.58

EMPLOYEE BENEFIT MATTERS AGREEMENT

THIS EMPLOYEE BENEFIT MATTERS AGREEMENT (this “ Agreement ”) is entered into on September 1, 2004, by and between PC Mall, Inc., a Delaware corporation (“ PC Mall ”), and eCost.com, Inc., a Delaware corporation (“ eCost ”).

RECITALS

WHEREAS, eCost is currently a wholly-owned subsidiary of PC Mall;

WHEREAS, eCost is considering an initial public offering of its Common Stock (“ IPO ”); and

WHEREAS, in furtherance of the foregoing, PC Mall and eCost desire to enter into this Agreement to allocate between them assets, liabilities and responsibilities with respect to certain employee compensation, benefit plans and programs, and certain employment matters.

NOW, THEREFORE, in consideration of the foregoing and the covenants and agreements set forth below, the parties hereto agree as follows:

ARTICLE I

DEFINITIONS

The following terms, as used herein, shall have the following meanings:

“Adjusted Option” shall have the meaning set forth in Section 5.1(a) of this Agreement.

“Administrative Services Agreement” shall have the meaning set forth in Article I of the Master Separation and Distribution Agreement.

“Affiliate” shall mean, when used with respect to a Person, another Person that controls, is controlled by, or is under common control (within the meaning of Section 414(b), (c), (m) or (o) of the Code) with the Person specified.

“Ancillary Agreements” shall have the meaning set forth in Article I of the Master Separation and Distribution Agreement.

“Board of Directors” shall mean, when used with respect to a specified corporation, the board of directors of the corporation so specified.

“COBRA” shall mean the Consolidated Omnibus Budget Reconciliation Act of 1985, as amended, and the regulations promulgated thereunder, including any successor legislation.

“Code” shall mean the Internal Revenue Code of 1986, as amended, and the regulations promulgated thereunder, including any successor legislation.

“Distribution Date” shall mean the date on which PC Mall’s interest in eCost shall be distributed, as further defined in the Master Separation and Distribution Agreement.

“Distribution Ratio” shall have the meaning set forth in Section 5.1(a) of this Agreement.

“eCost” shall have the meaning set forth in the recitals hereto.

“eCost Adjusted Exercise Price to Market Price Ratio” shall have the meaning set forth on Schedule 5.1(b) of this Agreement.

“eCost Employees” shall mean persons who are employed by eCost (including persons who would otherwise be deemed to be eCost Employees who are absent from work by reason of disability or leave of absence and inactive employees treated as such by agreement therewith).

“eCost Employment Liabilities” shall have the meaning set forth in Section 7.1(c) of this Agreement.

“eCost Flex Plan” shall have the meaning set forth in Section 4.2 of this Agreement.

“eCost Option” shall have the meaning set forth in Section 5.1(a) of this Agreement.

“eCost Option Plans” shall mean that certain eCost 1999 Stock Incentive Plan and that certain eCost 2004 Stock Incentive Plan.

“eCost Savings Plan” shall have the meaning set forth in Section 3.2(a) of this Agreement.

“eCost Welfare Plan” shall have the meaning set forth in Section 4.1 of this Agreement.

“ERISA” shall mean the Employee Retirement Income Security Act of 1974, as amended, and the regulations promulgated thereunder, including any successor legislation.

“Group Status Change” shall mean the cessation of PC Mall’s ownership of at least eighty percent (80%) of the combined voting power of all classes of stock entitled to vote or the total value of all shares of all classes of stock of eCost then outstanding. PC Mall’s ownership of outstanding eCost stock shall be determined pursuant to Sections 414 and 1563 of the Code.

“Group Status Change Date” shall mean the earlier of (i) the Distribution Date or (ii) the date on which the Group Status Change occurs, or such other date as PC Mall and eCost shall mutually agree upon.

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“Master Separation and Distribution Agreement” shall mean that certain Master Separation and Distribution Agreement, by and between PC Mall and eCost, of even date herewith.

“Offering Date” shall mean the date on which the IPO closes.

“PC Mall” shall have the meaning set forth in the recitals hereto.

“PC Mall Adjusted Exercise Price to Market Price Ratio” shall have the meaning set forth on Schedule 5.1(b) of this Agreement.

“PC Mall Adjusted Option” shall have the meaning set forth in Section 5.1(a) of this Agreement.

“PC Mall Employees” shall mean persons who, immediately prior to the Group Status Change Date are employed by the PC Mall Group (including persons who would otherwise be deemed to be PC Mall Employees who are absent from work by reason of disability or leave of absence and inactive employees treated as such by agreement therewith).

“PC Mall Group” shall mean PC Mall, together with all its wholly-owned subsidiaries, excluding eCost.

“PC Mall Option Number” shall have the meaning set forth in Section 5.1(a) of this Agreement.

“PC Mall Retained Employees” shall mean persons who, immediately after the Group Status Change Date, are employed by the PC Mall Group (including persons who would otherwise be deemed to be PC Mall Retained Employees who are absent from work by reason of disability or leave of absence and inactive employees treated as such by agreement therewith) but shall not include any persons who are or become eCost Employees on or after such date.

“PC Mall Welfare Plan” shall mean the “PC Mall, Inc. Welfare Benefits Plan” as in effect from time to time.

“PC Mall Savings Plan” shall mean the “Creative Computers, Inc. 401(k) Plan,” as in effect from time to time.

“PC Mall Stock Option” shall mean any option to purchase PC Mall common stock.

“PC Mall Stock Option Plans” shall mean that certain PC Mall Amended and Restated 1994 Stock Incentive Plan, as amended, and that certain PC Mall Amended and Restated Directors’ Non-Qualified Stock Option Plan.

“Person” shall mean an individual, a general or limited partnership, a corporation, a trust, a joint venture, an unincorporated organization, a limited liability entity, any other

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entity, and any federal, state, local, foreign or international court, government, department, commission, board, bureau, agency, official or other regulatory, administrative or governmental authority.

“Plan(s)” shall mean any “employee benefit plans” (within the meaning of Section 3(3) of ERISA), retirement, pension, savings, profit-sharing, welfare, stock purchase, stock option, equity-based, severance, employment, change-in-control, fringe benefit, bonus, incentive, deferred compensation, disability, worker’s compensation and all other employee benefit plans, agreements, programs, policies or other arrangements (including any funding mechanisms therefor), whether or not subject to ERISA, whether formal or informal, oral or written, legally binding or not.

“Plan Transfer Date” shall have the meaning set forth in Section 3.2(b) of this Agreement.

“Pre-Distribution Exercise Price to Market Price Ratio” shall have the meaning set forth on Schedule 5.1(b) of this Agreement.

“Securities Act” shall mean the Securities Act of 1933, as amended.

“Tax Allocation and Indemnification Agreement” shall mean that certain Tax Allocation and Indemnification Agreement, by and between PC Mall and eCost, of even date herewith.

“Welfare Benefit Plan” shall mean, any Plan providing welfare benefits within the meaning of Section 3(1) of ERISA.

Except as otherwise expressly provided herein, all capitalized terms used and not defined herein shall have the respective meanings assigned to them in the Master Separation and Distribution Agreement.

ARTICLE II

PRE-STATUS CHANGE PLAN PARTICIPATION

2.1 Continuing Participation in PC Mall Plans . Except as specified otherwise in this Agreement, or as PC Mall may otherwise direct, eCost shall continue as a “participating company” in the PC Mall Plans in effect as of the Offering Date, to the extent that eCost has not yet established comparable Plans of its own.

2.2 PC Mall’s General Obligations as Plan Sponsor . The PC Mall Group shall continue to administer, or cause to be administered, in accordance with their terms and applicable law, such PC Mall Plans, and shall have the sole and absolute discretion and authority to modify and interpret such Plans, as set forth therein.

2.3 eCost’s General Obligations as Participating Company . eCost shall perform with respect to its participation in the PC Mall Plans, the duties of a participating company as set forth in each such Plan or any procedures adopted

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pursuant thereto, including (without limitation): (i) assisting in the administration of claims, to the extent requested by the claims administrator of the applicable Plan; (ii) prompt payment of its allocable share expenses and costs relating to its participation; (iii) cooperating fully with Plan auditors, benefit personnel and benefit vendors; (iv) preserving the confidentiality of all financial arrangements the PC Mall Group has or may have with any vendors, claims administrators, trustees or any other entity or individual with whom the PC Mall Group has entered into an agreement relating to such Plans; and (v) preserving the confidentiality of participant information to the extent not specified otherwise in this Agreement.

2.4 Termination of Participating Company Status . Except as otherwise may be specified by PC Mall, effective as of the Group Status Change Date or such other date as eCost establishes a comparable Plan (as specified in Section 3.2 or otherwise in this Agreement), eCost shall automatically cease to be a Participating Company in the corresponding PC Mall Plan.

2.5 Terms of Participation for eCost Plans .

(a) Non-Duplication of Benefits . As of the Group Status Change Date or such later date that applies to the particular eCost Plan established thereafter, the eCost Plans shall be, with respect to eCost Employees, in all respects the successors in interest to, and shall not provide benefits that duplicate benefits provided by, the corresponding PC Mall Plans. PC Mall and eCost shall mutually agree, if necessary, on methods and procedures, including amending the respective Plan documents, to prevent eCost Employees from receiving duplicate benefits from the PC Mall Plans and the eCost Plans.

(b) Service Credit . Except as specified otherwise in this Agreement