I know what you need. The BD139 and BD140 are what you need.
You can also buy the originals as well.
The 1606 uses a 4080 chip to drive the outputs. What I meant was the 1606 is the amp still using the 4080 chip.
If you can order the BD139 and BD140 from your supplier that's what I would use. I have used them in numerous Hifonics amps.
The last 1606 I worked on used a 4080. Must be different versions.
There are plenty of suppliers out there as good if not better than digikey or MCM. If you will not use anything but them that does limit your ability to get parts.
Good luck my friend.