Maybe this answers part of your question.
text from another site (see link below)
Unfortunately, you get what you pay for. The other Halo Parasound amps only get my design contribution, shared with Taiwan engineers' attitude toward parts, construction, etc. The A23 is still a good amp in principle, but we have put a lot more attention into the JC-1.
http://db.audioasylum.com/cgi/m.pl?f...lo&r=&session=
this one too
These are similar designs on paper. It is like comparing a Porsche 924 to a Porsche 968. The JC-1 is more refined, mostly by Bob Crump with passive part selection, and Carl Thompson (formerly my Vendetta business partner) who did the circuit layout. The JC-1 is a successful experiment in amp refinement. All other Parasound amps do not have this refinement. Carl Thompson just got his JC-1's this week, and he has been using a modified HCA-2200 for years. There is a real difference, but not one that can be easily measured. For the record the HCA-2200 also uses FET's to drive the bipolar output devices. The only significant difference is that the JC-1 is all FET's, except for the bipolar output devices, and the 2200 has bipolar cascode and line drivers. While these devices could be swapped out for FET's, I doubt that it would do that much.
http://www.audioasylum.com/cgi/m.pl?...=halo&session=
