Ahhh... have been playing a bit again with emulators and another match for the issue -- it sounds quite like ReSID-fp+digi boost! (also distorted with filters switched off but that's distortion is more different)
So it can make standard digis sounds louder, but now it's overdrives the output.... (it will be a soft-switchable too later)
It look's like it could be backported...
Swinkels any help in here?