What is this black gunk?

@jean-paul Apologies! At first I was more concerned about the gunk more than specifics haha

It's a Luxman L-530 Integrated Amp

I'm very interested to take this board out and see what else might be blown in the circuit when I have the chance!

Also installing D-class is a very interesting idea 🤔 Might eclipse my knowledge but can't hurt to dig into it!
 
That PL-AD-160 module (choose the analog input version) needs a single 26V power supply. It lacks a unbal/bal converter though and it sounds best when driven balanced (actively). Could be done with just 2 dual opamps after the volume control.

If you will do this it pays off to first check the power transformer. You could be that unique guy that is the first in the world having exactly the right voltages. I keep believing this, you know.

Easiest is the older but still worthwhile 50ASX2SE if you can find one cheap. All in one board including PSU.
 
That PL-AD-160 module (choose the analog input version) needs a single 26V power supply. It lacks a unbal/bal converter though and it sounds best when driven balanced (actively). Could be done with just 2 dual opamps after the volume control.

If you will do this it pays off to first check the power transformer. You could be that unique guy that is the first in the world having exactly the right voltages. I keep believing this, you know.

Easiest is the older but still worthwhile 50ASX2SE if you can find one cheap. All in one board including PSU.
"Easiest is the older but still worthwhile 50ASX2SE if you can find one cheap. All in one board including PSU."
+1