Welcome Adam,
I'm with everyone else on the sub - minimum EP350 but bigger if you can. Keep in mind the EP350 and EP500 use the same enclosure, so size is equivalent for the WAF between the two. I have not heard the QS4's, but have the QS8's and can't recommend them highly enough. Lastly, as Cat said, look into a vertical center speaker if you have the space for it. Good luck.

Dan
On-Wall M5HP LCR, QS8 & EP500 in 7.1