That is an ATI 1504 four channel amp which drives the four surround speakers. The Audio Research amp drives the center in active bi-amp mode. The whole amp is heavily modified, and the channel which drives the HF compression driver is modified to work in triode mode.

The left and right mains also run in active bi-amplified mode with the LF being driven by the Dynaco MK IIIs (modified) and the HF compression drivers driven by the Cary stereo single ended triode amp (modified, with an outboard linear power supply for the output tube heaters). The active crossover I also designed and built with a crossover frequency of 500Hz

The four subwoofers (two for each stereo channel) are driven by a modified Soundcraft SA-1000 1000 watt amp.