I have two GFA-555II's, and they are very powerful, and will handle a 4 ohm load with no difficulty. They are pretty strong on bass reproduction, too, but my guess is that sonically, the very excellent McCormack DNA-.5 will be noticeably superior. Interestingly, I will (hopefully fairly soon) be comparing my 555II's to at least amps from Krell, McCormack and Theta (and possibly others) as I contemplate an upgrade for my 4 ohm Thiels. The Adcoms drive them just fine, but I am looking for a better sonic synergy match.
Tom.
Tom.