I would also recommend the QS8s with a room that size. The direct speaker in the rears can work well but only if you have the space to play around with their positioning. Most people have little 'easy' space behind their primary seating area.
The QSx speakers are simply fantastic for blending into the room, aesthetically and acoustically.
See my thoughts way back when on M22s vs QS8s for surround usage.
link here

"Those who preach the myths of audio are ignorant of truth."