I am wondering if it would simply sound wrong if you mixed a set of QS8 speakers for the side (main) surround speakers, and supplemented at pair of QS4 speakers for the rear surround to expand the sound field for Blu Ray movies with 7.1 sound.

I don't think I could afford two pairs of QS8 speakers. Would having a smaller set for the rear be problematic?

Anthem: AVM60, Fosi DAC-Q5
Axiom: ADA1500, LFR1100 Actiive, QS8, EP500, M3, M3comp, M5