Most bass amps will do just fine. The idea of separating the low freqs from the highs, in itself is a big improvement. Having a bass amp on the floor will give you a very close rival to an actual subwoofoer...if you're on a budget.

Remember - I proposed this as a budget alternative - not the standard or state of the art. It's a really good substitute for a dedicated sub powered by it's own amp and fed through a crossover.