I second Stanwal and Wavetrader, in particular in the context of your system. Bob's point is quite valid with satelites speakers or speakers with limited dynamics, but that would not apply to your particular situation of "full range" tower speakers. Running the signal through extra cables and crossovers will always affect it, usually by some form of loss, such as detail, image precision etc.
Given that you have a small listening room I am not sure if a sub would give you the improvement that you are looking for. You would need a real high quality sub and a precise setup to get this right. Have you considered a speaker upgrade instead? Good luck!
Given that you have a small listening room I am not sure if a sub would give you the improvement that you are looking for. You would need a real high quality sub and a precise setup to get this right. Have you considered a speaker upgrade instead? Good luck!