How important...

it's true, of course, that any high output amp will drive most subwoofers. the quality of the sound you'll get from your subs will, however, be affected by the quality of the amp you use. it is especially important in choosing an amp for bass/sub-bass operation to find on that is fast and carries high current as well as providing high output. i would be loath to use an amp on the lower ranges of my speakers that’s of inferior quality to that used on the upper ranges. IMO, the better the speakers, the more this applies. -kelly

I agree with Kelly. I have a biamped system (cross over at 125Hz). I'm using a class A amp for the bottom, just because I can't find the same quality amp in a switching amplifier. The switching really wouldn't affect the quality of the sound and it would run cooler (which I would really like)--but you do need two amps that perform at the same quality level if you have high resolution speakers and subs. The other thing to consider is how that amp performs on bass--some are better than others. I'm using a bass amp that has a high damping factor which works for my speakers on the bottom end. I also want the bass to have authority and not be soft at all--so that too played a role in my decision.

Ah, the old "who's on top" debate. I have found that being on the top is just as good as being on the bottom...it's all a matter of which brings you pleasure........

While I agree with all of the above posts (especially Sdcampbell!), I think that the crossover frequency plays an important part as well. If your crossover frequency to the subs were, say, 40 hz, you might not need an amplifier that is as sonically good as that for your higher frequencies, as there is not that much musical information that you can hear below that frequency as above--just make sure, though, that your bass amp can deliver the current and power needed to control and put out that bass. However, as you get higher in crossover frequency (my 4-piece system crosses over at 200hz), there is more audible musical information being delivered by your bass amp, and then matching both in quality and sonic character becomes more important, at least in my experience.

I thank everyone for their insight except sdcampbell :)