If you like the sound of your bookshelves and are just looking for a little more strength on the bottom end, a subwoofer is probably all you need. I would recommend running the speaker wire through the sub, then to your bookshelves instead of using the b speaker outputs. This will allow the sub to play all the low frequencies and send the rest to the bookshelves. If you have to have towers, try to find some Definitive Technology BP30s to listen to. They are being discontinued so you can probably get a really good deal on them (M.S.R.P. $1400). I have the smaller BP10Bs and have been completely satisfied with them. Getting a quality sub would be my first choice though and likely the least expensive.