I only have a 5 (Pro Logic surround). 5.1 or 7.1 may be
my next home theater system. I always set my front and
center speakers to small since I don't want them to
handle any frequencies they are not supposed to.
I let a subwoofer to handle the low frequencies. I
happen to have a chance to listen a pair of bipole
speakers. I can't say it is good or not, but different.
It is rather a personal taste. I don't know about
tripole. Give it a try if you can and see if you like
it.