I too was disappointed with the bass on my Vandy 3 Sigs and bought a sub woofer. A Velodyne 15 inch with a phase coupler for adjustable bass powered by 400 watt amp. I was using a 200 watt amp to drive the Vandersteens.
There in the garage now having moved on to Odyssey speakers.
There in the garage now having moved on to Odyssey speakers.