So you have acceptable bass extension with your current speakers but want more volume? What about padding back the mids and highs in the crossover and just turn what you have up? Save a lot of money. Seem to me that you could spend a lot of money just to alter the balance, not the bass extension of your speakers.
I have main speakers that are 3 dB down at 20 Hz and for audio they need no augmentation. I use powered subs only for video (when you need to get down to a felt but not heard 16 Hz for those low organ notes or exploding deathstars).
And while I agree completely with the guys that suggested planars and electrostats for the best mids and highs, mating a subwoofer to those is one of the most difficult tasks in stereo.
I have main speakers that are 3 dB down at 20 Hz and for audio they need no augmentation. I use powered subs only for video (when you need to get down to a felt but not heard 16 Hz for those low organ notes or exploding deathstars).
And while I agree completely with the guys that suggested planars and electrostats for the best mids and highs, mating a subwoofer to those is one of the most difficult tasks in stereo.