It's hybrid of tube voltage amplification section and Solid State (SS) unity gain buffer as output stage. The main point of design concept was to exclude the general negative feedback in audio path. However, you can find some similar realization in Anthem (partial match- uses NFB), Counterpoint, LAZARUS, Luxman (partial match), MOSCODE, Onkyo (partial match) amplifiers etc.
The trick and main difference is design of SS buffer - to reduce the heat dissipation, size and weight of the heatsinks and quantity of parallel output transistors. Most of the critical listeners noticed that large amount of parallel transistors in output stage. This may reduce some clarity in the voices and "air" as compared to the couple output devices. The other point is using Lateral MOSFET in output stage (Not the whole SS buffer) instead more affordable HEXFET MOSFET that Nelson Pass loves to use in his designs. Experienced listeners noticed that PASS amplifiers little bit "harsh" on the top-end.
The closest analogy in automotive design: to get more power from the engine we can increase size or number of cylinders, OR put the turbocharger in the motor. The 2nd way helps to get more power and keep the fuel consumption and weight of engine in acceptable range.
