Do you know this Apple document?

http://manuals.info.apple.com/en_US/0331009APMAVCG3.pdf

This is a description of the optional AV card. But I don't know if it's the same as installed in some 7600/8600/9600 Powermacs.

BTW the brown connector cannot be an ISA or PCI slot because there is no room left for a typical card. And: ISA slots use different spacing, PCI slots use different number of contacts, AFAIK.