@daveyf
The HK circuit can be worked on by anyone with an electronics background. The JR needs the modules. When I sent mine back, it came back to me as non-working and I had to send it back again. I have no skin in this game other then my own experience. I have personally met JR and he is a nice guy. To me both amps are great for the used prices. I can upgrade the HK easier that the JR but that is just me, the OP may do what ever he feels he wants to do as all of this is just the opinion of each of us and I don't think he can go wrong either way. Happy Listening.