Usually QS-8 Quadpolar surrounds are more amenable to easy placement in problematic locations. I prefer multipolar radiators because they typically deliver an excellent sense of envelopment even when mounted at uneven levels in a non-ideal location (my own setup typifies this).
On the other hand, larger spaces like yours are often more accepting of direct-radiating surrounds. I'd still choose the QS-8s but perhaps some Axiom buyers have had experience putting M22ti's at the rear in a surround role. Any comments out there??
Axiom Resident Expert