Update on the AWE64 Gold SPDIF output. First, here's what Creative states on page 12 of the AWE64 Gold manual (emphasis mine):
I can confirm that digitized audio will play via SPDIF under those conditions. For example, if you use Winamp to play a WAV or MP3 file encoded as 44.1 kHz 16-bit stereo, it will properly play back through SPDIF output. On the other hand, playing an Audio CD will not work, which makes sense, as the CD drive is connected to the AWE64 Gold using an analog cable.
Unsurprisingly, it seems that most DOS and even many Win9x era games do not output digitized sounds in 44.1 kHz 16-bit. In DOS, I tried Crusader: No Remorse and Duke Nukem 3D and neither of them played digitized sound via SPDIF. Duke3D even has an explicit 44.1 kHz setting for digitized audio under setup, but it still doesn't work. Under Win98SE, I tried running StarCraft and also got no digitized sound to play back via SPDIF.
Obviously, I haven't tested every single game out there, and it's possible that some of them do actually use 44.1 kHz 16-bit audio which will work. But so far, I think that the SPDIF Out of the AWE64 Gold is not very practical for gaming purposes. Sure, you can record pristine quality CQM and AWE music that way, and that's awesome. And Soundfonts loaded through the AWE Control Panel will also work just fine via SPDIF. Digitized audio is a gamble though, and will likely not work via AWE64 SPDIF Out most of the time.