Can I mount each power transistor on separate heat sinks?
Don’t do this. The amplifier will not be thermally stable. The four bias diodes should see the average temperature of all four output transistors. This occurs only when all transistors and all bias diodes are on the same heat sink. There is an exception. You can mount the two NPN output transistors for one channel on one heat sink and the two PNP output transistors on another. Either put all four bias diodes on one of the heat sinks or put two bias diodes on each. I once had a student who used 2 heat sinks per channel with two output transistors on each, a NPN and a PNP. He put the bias diodes on only one of the heat sinks. His amp was thermally unstable. The heat sinks without the diodes overheated. Putting both NPNs on one heat sink and both PNPs on the other solved the problem.
