Just updated and recompiled again to the latest SVN version - I'm not sure if this is also present in the last release or not, but the audio engine doesn't play back 48000 Hz properly.
If I go to the options menu and change the frequency, then restart the audio engine (clicking on the little icon), dropping to 22KHz or lower works OK (aside from the expected loss of quality), and the default 44.1KHz works fine, but jumping up to 48KHz results in audio tracks playing too fast at a higher pitch.
Don't know if it has anything to do with my soundcards, This is the same computer that multiboots my DAW on a different partition, so I have somewhat high-end "pro-sumer" soundcards, specifically two M-Audio Delta 192 soundcards running in sync together, and I'm testing the game with the standard 1/4' line outputs (not the S/PDIF) to my headphones. I'm using M-Audio's latest Windows XP drivers.
Can anyone with a different hardware setup confirm this?
Also, if it turns out to be the game and not my hardware, is the 48Khz even really necessary as a game feature? Most modern computers can play 44.1KHz just fine out of even their built-in soundcards, although I know of some cards (I think one is Sigmatel or something) that resample from 48Khz for playback, but I've seen those types of soundcards play back 44.1Khz files just fine in Windows Media Player and other apps.