That's odd...
you can hack the DOL-001 Gamecubes to add a digital audio port that work with all games.
it's an expensive hack as it requires a rare audio chip that can runs like $70 but I've heard of a few people having success with it.
Basically the digital video cable used for the japanese D connector and component video actually provides the audio and video digitally and the cable itself does a digital to analog conversion... the audio is in a rarely used digital format called "I2" so the hack basically converts the I2 signal to SPDIF...
it's only in the DOL-001 consoles since the digial AV port was removed for the DOL-101 gamecubes... no idea if the I2 signal is present in the Q models.
....
ok I just went to go dig up the old info on this topic and I guess you already know all about it:
http://forums.xbox-s...p;#entry3958977 
For some reason, I'm obssessed with the GC digital thing - never got around to building it as the chip was backordered when I tried to get it... oh well, on to other things