I guess I just don't really understand what's to gain by adding height channels to a music mix, unless it's incredibly dense music with dozens of layers (Talking Heads's
Remain In Light or Yes'
Close To The Edge, for example). If anything, I suspect it'll just make everything sound muddled and less discrete - it's not like they're gonna mix lead guitar in the ceiling.
Interesting
quote from Elliot Scheiner regarding formats beyond 5.1:
For me, the thrill of a good discrete mix is being able to pinpoint all the instruments. It's easy enough to just "fill the room" using a stereo source and a good decoder or DSP.