The most important attribute of a dedicated audio room is that it's dedicated to your audio enjoyment. Set it up as you like, listen when you want, listen to what you want, and (if effectively insulated) listen as loud as you want. Size/shape is secondary (unless it's closet sized
).
OTOH it seems that you have plenty of speaker for the given size of room, but that allows you to trade large speakers for smaller quality speakers (especially already having a subwoofer).
