Welcome Gary,
First the QS series speakers are not dipoles. Dipoles have their drivers wired out of phase. The QS series drivers are wired IN phase, so they are really bipoles x 2 which = quardrapoles. They are the best surrounds I've ever heard.
If you are the least bit interested, now or in the future, in SACDs or DVD-As, then you should seriously consider going with the M2s as rear surrounds (The M3s are generally considered tonally similar to the M40s and M50s, and tonally different from the M2, M22, M60, M80 series). Direct radiating speakers, like the M2, are recommended in a 5.1 set up for listening to SACDs and DVD-As. For 7.1 movie watching they will serve admirably as rear surrounds, with the QS speakers, or 2 more M2s as side surrounds.
If you have no interest whatsoever in SACDs and DVD-As, and primarily watch movies, then 4 QS series speakers would be incredible as surrounds. They will diffuse the sound which, in my opinion, is the whole point of surround speakers: to surround you with sound. There are however, many who don't agree with me and prefer direct radiating speakers as surrounds.
You say you like to localize the sound. If that's what you prefer, you should consider going with direct radiating speakers (M2) as all 4 surrounds.
But I would state that, of the Axioms I own (M60s/VP150/QS8s), the QS8s do what they were designed to do the best.
