Thanks.
Very interesting.
I was thinking, "Hey! Wait! Why am I converting this amp to 4-board "balanced?" " And reading in this thread has convinced me that additional sound quality improvement, if any, would be quite minimal and probably inaudible to me.
I bought all the additional amp board parts and also the parts for a second sigma PSU. I have an extra Beta amp board laying around too, with bad output transistors on it; so now I just fix that, build the other channel and Sigma pSU, and I have a 2-channel Beta to sell. I even have a Par-Metal case laying around someplace.
I get all the fun of building it (I really like building stuff) and then I get the money back that I put into the parts and the time. This one, I am going to make it pretty. I wonder how a 3/16" (or even 1/4") thick polished copper front panel would look on the Par-Metal box? I am partial to copper. Maybe add bubinga wood cheeks to the case, too. Bubinga and copper are a really nice combo.