And one more thing . . .
open the windows if you can. This will allow more of the sound to escape from the room, which is a good thing.
I wouldn't worry about noise from outside -- the drums are loud enough to where that shouldn't be a problem.
Coloradojay, drums are a very low-mid and bass-heavy instrument -- kick and snare reside from 500 hz, generally, all the way down to 40 hz and even some subsonic stuff from the kick.
Lowmid and bass frequencies are very difficult to tame. You can't just hang blankets or put up foam. And they cause all sorts of problems in a room like TamaSabians. The room dimensions and layout come very much in to play, and low ceilings and paralell walls are basically the culprit.
What happens is the higher frequencies from the cymbals are very easily absorbed by whatever blankets, furniture or other absorbant material you might hang, etc. While the bass frequencies (and low-mids), on the other hand, kind of go through any material you put up and just bounce all over the place willy-nilly and make everything sound muddy / tubby / or boxed in. That's kind of an oversimplified way of describing a very complex phenomenon that could otherwise take up chapters worth of explanation or study.
Having large windows is good, because it does give some of those problematic frequencies a place to escape. Very thick, dense insulation panels like corning 703 or mineral wool -- hung from the ceilings or surrounding the kit (perhaps some extra sofas would help out, too) -- can help absorb some of the lower frequencies, also, and make everything sound tighter.
In Tama's case, the fact that he's using a very minimal micing technique and (I'm assuming) close-micing can help minimize some of these effects . . . but it's still one of those things where you never realize just how much better and clearer everything sounds untill you actually make the move and improve those accoustics.