Dklap- The Hsu amp/sub combo must have some kind of feedback or servo control, otherwise, amp would not make a difference. You might try looking for an NHT mono sub amp, they have variable crossover and generally are pretty cheap used. Also maybe an NAD that you can bridge to get higher power, if you are willing to live with the fixed crossover from your receiver. However, Hsu sub/amp combo has had great press. Might be worth the $.