I imaging the reason a Mac version card is needed is that the Sun firmware is 128K. If this is the case, you can check out this article to see how to replace the firmware chip on a regular PC version with a larger capacity chip.
http://www.darkness.uklinux.net/
My
computers
(incomplete)
Octane R10000 225MHz, 2GB RAM, 1x36GB HDs, 21" monitor, SSI (no TRAM) graphics
SGI Indigo 2 R8K75 TEAL Extreme 256MB,
SGI Indigo 2 R10K 195 Solid Impact 256MB, MAX Impact Pending