I agree that without rearranging the room, 5.1 would be the way to go. QS10s will give you more dynamic range. Since you already have your towers you can tell what the dialogue sounds like without a center channel if you don't already have one.

LFR1100
VP180HP
EP600
M3 In Ceiling x 4
M5OW
M2 - Atmos rears
ADA1500.5
M3 Outdoor Speakers
ADA 1000.8