In fact, mp3s cannot have more than two channels, so even if you found something that was quadrophonic (which is rare, at best), mp3s wouldn't be able to encode all that information. I don't think WAV or FLAC have facilities for more than two channels, either. CDs certainly don't. The Ogg Vorbis format does, but I think it's currently unimplemented.

Of course, add onto all of that that the empeg doesn't have the capability of producing more than two discrete outputs (which are then split before preamplification), it's kinda moot anyway.