His tone is extremely stiff and hi-fi. That is what he was seeking when he switched to using McIntosh amps. He did not want the characteristic sag, compression, and back EMF of a cranked up tube amp. A clean tube preamp (the AB763 preamp is pretty darn clean by itself) into a highly-damped solid-state hi-fi amp is little better than a solid-state preamp into a highly-damped hi-fi power amp. What makes a tube amp sound louder than a comparable solid-state amp is voltage overshoot due to poor damping factor. Damping factor is the ability of a power amp to control speaker cone movement. In a poorly-damped amp, the cone is not tightly controlled by the power amp. The result is that the speaker starts to create its own signal, which is fed back into the power amp (back EMF) where it combines with the signal coming from the preamp. Back EMF is what makes guitar tube amps sound so different with different speakers. Global negative feedback is used to increase damping factor, making the difference not as severe, but a tube guitar amp is woefully under damped compared to a solid-state hi-fi amp.