Most music is 2-channels, else you are looking for DVD/DVDA or SACDs that can be multi-channel (typically 5.1).
You should probably better look at some audio forums for a a good multichannel source, and compare to the 2 channel version.
PS: looks like a good place to start :
http://canadahifi.com/forum/showthre...ecommendations
PPS: not sure that all sources can be played in you car though, make sure to check first
