I FINALLY got a chance to look at this. Interestingly, the Power Macintosh 6500 and the 20th Anniversary Mac have IDENTICAL ROMs. MD5 produces the same checksum for each. The code in the ROM must detect whether it's in a 6500 or a TAM. I ALMOST wonder if it's possible to trick it somehow and have a 6500 play the TAM startup sound.

It seems like because the ROMs are identical the two machines should have the same gestalt ID, so it may be detecting this some other way.

I have a Power Mac 5500 but I have not ripped the ROM and it's stored where I can't get to it right now. But when I get the ROM off of that one, I'll be sure to let you know how that one compares.

I really thought for some reason the ROMs would be just slightly different at least because of the startup sound, so this is kind of interesting.