You should try Wayne's multi sub trick. It takes things up a level or two.
I've been playing with flanking subs and a distributed (rear) sub with a pair of 2 Pi Towers. The addition of the subs, setup as Wayne suggests, takes the sound quality up quite a few notches.
Two of the subs are inexpensive and the other is a REL that I picked up used. There isn't big money in this setup.
Frankly, the towers sound fine against a wall by themselves. But adding the flanking subs helps subdue a few frequency notches and also allows the speakers to be pulled away from the wall. They seem to image a bit better away from the wall and the flanking subs make up for the bass loss and help smooth the bass.
Adding the rear sub further smooths out the bass and makes it cleaner and clearer. It's not a subtle change.