Used to occasionally run into similar problems. Game changer for me was putting a Micro Thumpinator on my board. It cuts out all of useless frequencies below 37Hz (I think) which suck all the power out of your amp and cause the drivers to flap about, potentially causing severe damage. Wouldn't be without it now because it focusses the sound right where you need it. I'd also look at pushing the mids in the EQ to try to get some more cut through.