Rel sub

@fertguy One sub NEVER works well. You wind up with a disturbing modal pattern in almost any room, bass here, none there. Creating accurate bass below 60 Hz Also requires a lot of acoustic power which requires surface area (big drivers) and long excursions. Mono amps for the main speakers has nothing to do with it. The same situation results with a stereo amp. Read my Building Resonance Free Subwoofer thread below. The fact is you are better off with no subwoofer than a poorly implemented one. Aside from at least two subwoofers you also need a complete two way crossover. The low pass filter most subwoofers come with is inadequate. 1/2 the advantage of using a subwoofer is relieving the main speakers from having to produce low bass resulting in lower distortion levels.  If cost is a factor you can always stage your subwoofer system. Subwoofers done right are the difference between a live performance and just another stereo.