Jonathan
I would advise you read the following thread It seems poor connections at earth spades and signal earth are known reasons for the board going into oscillation and self destruction
Damaged NCC200-Left | pink fish media
If problem still persists then some investigation will be necessary
Google the "Dim Bulb Test"
Can you power the amp via an incandescent light bulb (60watts would be good) to effectively drop the applied mains voltage. Be careful with mains wiring Insulate everything properly etc
If this stops the smoke then it is likely that your bias current is too high.
This is most likely due to the applied relatively high DC rail voltages of 53.5 volts from your Cap6 boards
You may get away with reducing the bias current by rotating the bias current setting variable resistor on the board
It is a small blue component in the middle of the board labelled Set Bias
You could try turning the little screw anticlockwise to reduce the bias current. If I remember correctly the NCC 200 should run at approx 100mA which gives a voltage of 22mV across the 0R22 resistor
You will not be able to reach this value with the bulb in series but at least it will give us some idea of what is going on
The other possibility is that your wiring configuration ( it does look a bit messy) is causing some coupling between input and output which is causing the board to go into oscillation
I would add that I sold you the boards in good faith believing them both to be in proper order (although I never tested the repaired board) as I had already fitted my NCC220 replacement boards
I'm happy to refund you if that's your preference as long as you don't totally destroy them. I think though that it would be unwise for you to plug in some new boards into your existing setup as there is a real risk you would damage them. Best persevere and find what is going on with your current setup
eddie