Welcome NegativeC,
The QS series speakers are the best surrounds I've ever heard.
FYI, the QS series are not dipole speakers. Dipoles have the drivers wired OUT of phase. All the drivers in the QS speakers are wired IN phase making them like bipolar speakers. But, there are 4 drivers in the QS speakers, so they are bipoles x 2 = quadrapolar speakers.
As you say, there is a debate as to whether direct or polar speakers are best in the surround role. It is my opinion there is no "best." It just comes down to your personal preferences. There are those here who use directs, and some who use polar speakers. I fall into the latter category, and I LOVE my QS8s.
However, as for a single speaker in the rear surround position, the consensus is that it should be polar speaker, because with one direct radiator in the rear, it's sound seems to come from the front rather than the rear. I have a direct radiator in the rear (I didn't know better when I installed it), and that is how it seems to me (I have no idea why this is so).
I don't think you need worry about the lack of bass response of the QS series. Your subwoofer will be putting out plenty of bass, and bass is non-directional so you won't be able to tell where it's coming from.
It would be a good idea to give Axiom a call and ask them your questions. They're just plain folks who will be glad to help without trying to talk you into something you neither need nor want.
Just my $.02.
