Im not sure you're going to solve the bass problem just by throwing more power at the speakers. Placement and your room can have quite an effect on these speakers. I improved the bass on my 4a's by placing them against the long wall and putting a large rug on the floor helped too. Im not saying that an amp change wont help with the lower frequencies, but its not all about the power. I bought an fpb 200 for about $3000 and the bass was incredible. Unfortunately, the top end was too harsh for me. I stepped up 150 watts to the Pass X-350 and the overall improvement was astounding but the bass was a little shy compared to the krell.
Heres an idea, sell your 4's, spend $1000-$1500 more for the 4a's The bass will be much improved and youll save about $4000
Heres an idea, sell your 4's, spend $1000-$1500 more for the 4a's The bass will be much improved and youll save about $4000