This is custom amp that Dustin bought off Craigslist. I don't remember the cost, but it may have even been free!
Dustin took it apart and it appears to be two plate amps put into a single enclosure. The front of the box has crossover and gain controls for each channel, and the back has phase and an RCA input for each channel. Each side has a very large aluminum heat sink.
Under 20hz the amp has pretty severe roll-off on its inputs. From 20hz to 10hz, and I had to increase the main volume by almost 20db! At 5hz, even by just 30Vpp of output on the amp, I was at +10 on my preamp and output clipping was starting on the RCA output of the preamp. The 5hz test was aborted for that reason.
I didn't test the output with both channels driven simultaneously, but both channels driven independently had exactly the same output down to the single volt.