You unfortunately failed to mention if the error occurs with the Parity Error
Checking enabled or disabled.  I assume you mean it gives you a parity error
when it's enabled, and not when it's disabled.  How high will the count go on
the memory check at boot-up before this error occurs?  Does the system beep
at all; if so what's the pattern of beeps?  The error could be occuring in
Cache memory (not so likely) or video memory, as well as the simms.

The fact that you have AMI bios is not conclusive in determining the board
manufacturer either.  Boards are made by thousands of small Taiwanese companies
(among others) that buy the name brand chips and put them together with some
simm sockets to make your board.  I tend to doubt your problem is with your
IDE controller, also.

Anyway, perhaps if you answer those questions someone can help you out better.