It's almost impossible to make a room in a house sound proof without spending an arm and a leg. There are these foamy tiles that are about two or three inches thick for walls, ceiling and floor which tone down the bass and heights a little but if you really want to make it sound proof, you have to do way more than that.
Just use a good pair of headphones, even a high-end version is cheaper than padding up your studio.
Oh, and Nick from Sonicstate has uploaded a presentation video of the new Korg Electribe, watch it here:
Not a very good presentation I may add, but hey. Apparently, the unit CAN be used standalone (without computer) so that's a good thing. They also added the Korg Quad Pad effects and various other things. The small sound demo on the end sounds good (albeit a bit too new-style electro-esque for my taste), guess I have to give it a try when it's out.