Pretty sure that an audio player's only option for lowering volume levels comes in the form of digital attenuation which isn't a good thing. This isn't a problem I've ever run into, I can't figure out why your games play at such a lower volume than your music.
Wait, I did run into a funny situation where using the toslink out on my X-Fi gave me lower sound levels than USB, and changing windos sound level changed the volume of my DAC/amp. I tried this first under WASAPI and froze my computer for some reason. I was only experimenting at the time, so I swapped it to use direct sound, and found the audio coming from the player to be just as quiet. Are you using an external Dac/amp, or is it coming right out of your computer? If you've got an external DAC, you could set foobar to use a different input as a reminder to change your volume level, nothing would play until you switched inputs.
Oh, wait, Xonar right into HD-600's. I imagine what's happening is somehow related, the game's audio is being lowered by some setting but the audio player is skipping it because of WASAPI. Is windows sound turned all the way up?
Edited by Phos - 1/1/12 at 2:27am