Compare the original artist's versions to the versions recorded especially for GH3 and you'll notice that the Wii version of GH3 is outputting the tracks in MONO sound only.
How very 1932. Mono, not even stereo let alone the advertised Dolby ProLogicII!
check this thread: http://www.guitarhero.com/forums/8/forum_topics/1258
We're being ripped off.