Check out Vandersteen 2Wq subs. Probably the best for integrating with your main speakers. They are unique in that they connect to your amps speaker terminals and this in part is why they integrate so well. From the Vandy web site:
Conventional powered subwoofers receive their input signal directly from their crossover before the main amplifier. The sonic signature of the main amplifier that is an important part of the sound you hear from the full-range speakers is missing from the subwoofer. This causes blending and integration problems as the sonic characteristics of the system are different above and below the subwoofer crossover point. This deterioration of system coherence is why conventional subwoofers have never been totally accepted as part of ultra high-performance audio systems.
The 2Wq uses a unique, innovative connection method that reduces the current demands on the main amplifier, but leaves the main amplifier in the signal path to the subwoofer. The system realizes the benefits of bi-amplification with absolute sonic continuity as the main amplifiers characteristics that are evident through the full-range speakers are maintained to the deepest bass, but with the power and control of the 2Wq s internal 300 watt amplifier.
Complete description: http://www.vandersteen.com/pages/2Wqlit.html
Conventional powered subwoofers receive their input signal directly from their crossover before the main amplifier. The sonic signature of the main amplifier that is an important part of the sound you hear from the full-range speakers is missing from the subwoofer. This causes blending and integration problems as the sonic characteristics of the system are different above and below the subwoofer crossover point. This deterioration of system coherence is why conventional subwoofers have never been totally accepted as part of ultra high-performance audio systems.
The 2Wq uses a unique, innovative connection method that reduces the current demands on the main amplifier, but leaves the main amplifier in the signal path to the subwoofer. The system realizes the benefits of bi-amplification with absolute sonic continuity as the main amplifiers characteristics that are evident through the full-range speakers are maintained to the deepest bass, but with the power and control of the 2Wq s internal 300 watt amplifier.
Complete description: http://www.vandersteen.com/pages/2Wqlit.html