6.1 and 7.1 are useless believe it or not.
nothing is coded further than 5.1.
the receivers do a very good job of improvising those channels, but as for anything made current-day, 5.1 is the most they'll do.
don't let that discourage you from buying a setup like that, but if it costs monstrously more than a 6.1 or 5.1 (and a good one, at that) then i wouldn't push for it too much.
