Big Black Box.
With Unity Current Interface made to measure for the Unity Gain Interface output of the PRA-1100 preamplifier - a way to upload to amplifier's input to lots of gigaOhm for perfect immunity to loudspeakers tortures.
Also a Double-Super-Non-NFB circuit, Dual-Mono structure and up to ±500V/µs of slew rate - big black box.
Curiosity of the (late) times : the Direct CD input is adorned with a high pass filter !
Sometimes available with optional wood sideburns (for much better looks), the POA-2200 isn't that rare nor that easy to find, but it is a big black powerful box nevertheless.
However, specifications point out that A & B speakers must not run below 6 Ohm and A + B speakers below 12 Ohm...