DEFINITELY THE PARASOUND OFFERINGS!!!! Most of the Parasound models offer adjustable input volume pots, and are simply superb bass amps! Infact, the Parasounds, if anything, are really well known for their solid bass reproduction! The are very good sounding solid class B amps on their own mostly, but also shine when used to driver bass on biamp and subwoofer set-up's!
If you are doing it right, you could use a very high refined amp on the top, and the parasound on the bottom, for absolutely superb results in just about every conceivable instance!...that being if your speakers sound good biamped in the first place!