Do not know them. But used to work on old tuner, receivers, amps, and integrateds. That was 25 - 30 years ago. It was difficult to track down noises. Sometimes even changing the position of a part caused stability issues.
Especially circuitry like split phase amplification. Very finicky sometimes.
A modified unit might be perfect. Or might be a life long project to sort out. Without knowledge of all changes it can be very time consuming to trace out all circuits and interactions.
The receivers are the worst. The amount of circuits in the signal path is unbelievable. Tone controls, boosts, balance, and switching can kick your butt. Especially with this gear getting close to fifty years old.
Casper might not have the greatest business communication skills. Most one man shows struggle with this. That is one of the reasons they are a one man show.
But if he is refurbing units and cranking them out he is a needed resource.