I've tried getting passthrough to work on both my Creative soundcard and my onboard audio and it seems that in Crysis, Fallout etc.., it defaults to stereo and if you want to do true surround sound it isn't possible. The closest you can get is one of the pseudo-formats, neural, multi-channel stereo, etc..
Maybe it is what pandora is outputting that is colored. It sounds just fine on my shitty pc speakers at work but when I get it home and run it over my more revealing synchrony ones it seems heavily colored, thick in the mid-bass and low bass. WMP files don't seem altered as badly. This happens with both my creative and my on-the-motherboard adapter. I think I've got pass-through to work with both of those. High bit rate is selected.
In any case, until they mix surround sound on the games that I play in a standard format, true multichannel may not be possible. Seems at least Fallout Vegas and Crysis default to stereo output when preamp is set on "auto detect". Maybe there is a workaround in some of the game's .ini files to get it to output in a true lossless surround sound format.