I have a YST-SW315 in an 800 cu. ft. room. No matter what I did, it sounded like total garbage when I first put it in there and did my best to dial it in.
After advice from Serenity_Now on how to re-arrange my room, adding in some sound panels I acquired from him and some touches of my own, that sub is now TIGHT, TIGHT, TIGHT! It's a 2-channel, music only room with bookshelf speakers but because of its lay-out and treatment, it sounds better than my home theater for music.
So play around with the room and don't be afraid to throw in some temporary furniture and cabinets that can act as absorbers and diffusers to gauge how the sound changes.
