Well as luck would have it, Apple has open sourced much of their core operating system, including the driver for USB audio, as part of their Darwin project. So I downloaded the AppleUSBAudio-199.2.10 archive.
Getting it to compile was a bit of a chore, as they are transitioning towards using real 64 bit integers for things like time stamps, so I had to cast this and that, and change a few variable types. I haven't actually figured out how one installs a driver in place of its original.
But I did notice something strange, a probable bug that might lead to the driver not recognizing if a device could support an S/PDIF connection. In the AppleUSBAudioEngine::AddAvailableFormatsFromDevice method there is a for loop
for (altSettingIndx = 1; altSettingIndx < numAltInterfaces; altSettingIndx++) {
...
}
and then after the for loop, the altSettingIndx variable is used again to test for an S/PDIF interface, but I don't think it's a valid index and it looks like the test was supposed to be in the for loop.
I'll try to find someone at WWDC to confirm this is a bug.
