I design rooms with multiple subs often. I agree with Rives about using two subs and room modes. They know what they're doing. This is one of the hardest things to get right in any home theater. I really dislike locating a sub that's near my seating area even if the bass is great. I strongly believe that the room's low frequency room behavior needs to be looked at first (test the room, our ears can easily deceive us) and a few questions answered:
1) Were you happy with the bass except for the low output? If you were happy except for the output I'd get another bigger sub and try it out using the processors crossover. The then play around with placement if needed.
2) The Vandersteen needs it's own crossover and your main L/R amplifier as per it's instructions unless you carefully changed it's hook up. It makes it hard to use it as an LFE.
3) If you still want to use two Vandersteens (or any two subs), although very good subs, their hook-up make them problematic to use. I'd probably try two identical of a different brand. I'd need to carefully set them up by taking measurements which can be done with a simple Radio shack meter, a free audio generators through your computer as a source or a very good CD that has very closely spaced frequency bands and a piece of graph paper. It's time consuming but very enlightening about bass performance.
1) Were you happy with the bass except for the low output? If you were happy except for the output I'd get another bigger sub and try it out using the processors crossover. The then play around with placement if needed.
2) The Vandersteen needs it's own crossover and your main L/R amplifier as per it's instructions unless you carefully changed it's hook up. It makes it hard to use it as an LFE.
3) If you still want to use two Vandersteens (or any two subs), although very good subs, their hook-up make them problematic to use. I'd probably try two identical of a different brand. I'd need to carefully set them up by taking measurements which can be done with a simple Radio shack meter, a free audio generators through your computer as a source or a very good CD that has very closely spaced frequency bands and a piece of graph paper. It's time consuming but very enlightening about bass performance.