I have to toss my hat in to the ring as well. I just migrated to a new PC I built, so all of my drivers are up to date. My old PC ran 1.5.2 without any problems, but the new build is completely without sound. From the log:
00000.518 INFO SOUND: loaded 1074 sdefs from "sounds\sdef"
00000.593 ALERT SOUND: Can't start XAudio2.
00000.593 ERROR SOUND: can't start renderer
Hope you guys have some luck because it's unplayable without sound.