I just did some calculations on how much power the NAD will deliver in class A into 8 Ohms, with a bias current of 100mA. It seems it is a whooping 0,08W peak! I may try, over a period, increasing the bias current to 500mA to give about 1W class A. I did add to the cooling after all.

Note: I tried upping the bias current to 250mA, but the heat sinks were warmer than I liked, and I have backed down to 125mA.