File this under "why didn't I try this sooner?"
Short version: I played with the wavelet sharpening function in registax. This happened:
Left: unprocessed output after stacking in AutoStakkert of sun in H-alpha. This is representative of the raw output of single frames other than the lower noise.
Right: after loading file into registax and randomly playing with wavelet settings
I think it no understatement that this makes a night and day difference for surface detail, which is otherwise lost in the low contrast. Previously I have tried different methods like aggressive unsharp and even HDR techniques to try and bring it out with varied success.
This deliberately higher exposed shot of the same region was intended to bring out the prominences. They're visible even before processing, but after it sharpens up nicely.
In both cases there's some issues with bright/dark rings on high contrast edges like you would get with unsharp, so I'll have to play about with optimising that some more.