Discrete double MCS+. The transistors are bipolar NPN and PNP types.
To the right the discrete input instrumentation amplifier. To the left output with mosfet switches.
Accuphase started to use discrete input instrumentation amplifier in A-200.
Also A-70 and now M-6200 too.
P-4200, P-6100, A-36 and A-46 uses opamps, discrete is so much better and all this amps will have it I think in the next upgrade.
Also all the integrateds uses opamps input instrumentation amplifier.
Having had the chance to listen to Accuphase gear many times at David Baskin's place, I am always constantly amazed by the looks, feel, and sound of Accuphase. I fing them to have the best build quality of any gear I've seen.