Then look at a Counterpoint SA-100 (the SA-220 is more complicated with a lot of extra, unused circuitry).
What I would change is the horrible output stage - you have to using those depletion Mosfets anyway. Drive the gates with another stage to get the low impedance required to charge and discharge the gate charge. It will work with a high impedance driver, but not very well considering distortion. Grounding the gates isn't what you want to do either, but using a DPDT replay to provide heavier negative gate bias during start up would kill start-up and shut-down noise. If you elect to leave the output normally biased during up and down transitions, you might want to short the signal path to the output stage drivers.
Good luck with this. I would love to see what you come up with!
"Just because you can, doesn't mean you should" © my Wife