<PAGE>
 

                                                                 EXHIBIT 10.7(c)

[LETTERHEAD OF MARINE MIDLAND BANK c/o HSBC BUSINESS LOANS, INC. APPEARS HERE]




                               October 31, 1996





Number Nine Visual Technology Corporation
18 Hartwell Avenue
Lexington, Massachusetts 02173
Attn: Daniel W. Muehl, Chief Financial Officer


Gentlemen:

      Reference is made to a Loan and Security Agreement between Marine Midland 
Bank, as assignee of Marine Midland Business Loans, Inc. (the "Secured Party") 
and Number Nine Visual Technology Corporation (the "Debtor") dated December 10, 
1992, together with the Second Consolidated and Restated Amendment dated March 
27, 1996 (hereinafter referred to collectively as the "Agreement").

      Notwithstanding the provisions of the Agreement, it is agreed, effective 
immediately, that the Agreement shall be amended as follows:

      Item 30(b) of the Schedule attached to the Agreement is hereby stricken in
its entirety and the following new Item 30(b) substituted therefor:

      "(b)  Minimum Tangible Net Worth: Debtor shall at all times 
            maintain a Minimum Tangible Net Worth in an amount not 
            less than $23,500,000.00 for the quarter and for the 
            fiscal year ending December 28, 1996, and for each 
            subsequent fiscal year to be not less than the amount
            required for the prior fiscal year plus seventy-five 
            (75%) percent of the Debtor's net income earned for 
            the current year, after provision for taxes, provided 
            that there shall be no reduction in the required 
            Minimum Tangible Net Worth for losses.

            "Tangible Net Worth" means the sum of stockholders' 
            equity plus the principal balance of any debt that is 
                   ----
            subordinated to Secured Party in a manner satisfactory 
            to Secured Party, minus the book value of Intangible 
                              -----
            Assets (as defined below), all determined in accordance 
            with generally accepted accounting principles 
            consistently applied.

<PAGE>
 

            "Intangible Assets" means (1) all loans or advances to,
            and other receivables owing from, any of Debtor's officers,
            employees, directors or members of their families or owing
            from any of Debtor's subsidiaries or affiliates, (2) all 
            investments, whether in a subsidiary or otherwise, (3) goodwill,
            and (4) any other assets deemed intangible under generally
            accepted accounting principles."

      Kindly note that the alterations to the Agreement contained herein do not 
in any way alter, releases or change any other sections contained in the 
Agreement.

      Please acknowledge your agreement to the foregoing by signing the enclosed
copy of this letter and returning the same to the undersigned.


                                         Very truly yours,

                                         MARINE MIDLAND BANK

                                          
                                         By: [SIGNATURE APPEARS HERE]
                                            ---------------------------- 

UNDERSTOOD AND AGREED TO:

NUMBER NINE VISUAL
 TECHNOLOGY CORPORATION


By: /s/ Daniel W. Muehl
    ----------------------------------------
    Daniel W. Muehl, Chief Financial Officer   


                                      -2-