One problem I see is that you are sitting a bit far from the speakers, so they would ideally be further apart than you have room for. The problem is the wall on the right side; you don't want to put a speaker too close to it, yet you want to get those speakers as widely apart as possible. As for side surrounds, you might as well go for in-ceiling speakers or ceiling mounted speakers, because you don't have the right distances or mounting heights for placing those speakers on the wall. In fact, you might just think about sticking with a 5.1 system, or maybe Atmos 5.1.2.