Hi Paul, If you haven't tried using both A and B speakers outputs at the same time with your two sets of speakers, what's the hold up :-) From my experience, you will find the La Scalas outshine the Heresys, but still sound good. If you can run a long test of loud volume and monitor your amp and all is good, you are set. If you still want more volume, then yes, separate amps would be necessary. You may also want to consider a subwoofer or two.