I just re did my garage it's 18x18 feet.
Fully carpeted and insulated. I did this for my 3 small boys, it's their bedroom as well. The theater is not directly center wall but over to one side.
I'm using a older bkavr507 7.1.
Speakers are lsi polks 4ohm with a older SVS PC ultra sub..
I'm tempted to buy another 2 rears to complete my 7.1.
My surrounds now are directly to the sides of the listener.. Polk lsifx di and bi.
I use a ps3 soon to be ps4