I have 2 12" RE XXX's and they are both running off hifonics 2600 watt amps. While other amps might make a little bit of difference, for the price hifonics is a great amp. I would start by double checking the phase and tunning. They just are low end mosnters, no matter how you tune your amp or build a box, you might not get exactly what you want out of the high end!!!