Hello,
You can add subwoofers for two channel stereo. If your two channel preamp does not have a subwoofer option you can run your speaker wires from your amplifier to most subwoofers and another set of speaker wires to your front L/R speakers and use the crossover controls on the subwoofers to decide what you want the frequency cutoff to be. A popular place is 50 hz as long as your front speakers can do 50hz. REL, SVS are a few popular names but even cheaper lines have this option. This way your fronts do not have to work as hard and get a lot more detail since they are not trying to go down to 20hz but most speakers bottom is 30-40hz. I prefer sealed subs for music since they produce more detail. The ported subs are great for home theater to get the room shaking with less power.
You can add subwoofers for two channel stereo. If your two channel preamp does not have a subwoofer option you can run your speaker wires from your amplifier to most subwoofers and another set of speaker wires to your front L/R speakers and use the crossover controls on the subwoofers to decide what you want the frequency cutoff to be. A popular place is 50 hz as long as your front speakers can do 50hz. REL, SVS are a few popular names but even cheaper lines have this option. This way your fronts do not have to work as hard and get a lot more detail since they are not trying to go down to 20hz but most speakers bottom is 30-40hz. I prefer sealed subs for music since they produce more detail. The ported subs are great for home theater to get the room shaking with less power.