You could take the .MOD and run it through a higher quality renderer. The biggest improvement would be using high quality resampling, as the resampler in Paula is very low quality. This should improve all pitch shifting or pitch related effects. You could also render to 48 kHz, which might improve things a little bit for those samples that are getting pitched shifted up enough. You would also render to 16 bit, but that wouldn't actually give an improvement over what you would be hearing out of an Amiga, it would just make sure it's as good as the Amiga.
I don't believe Paula even
does any interpolation "resampling" - I think it just switches from one sample value to the next. TBH, that's how I prefer it (I've never found interpolation to be an improvement, at least not on OCS Amiga-era MODs,) and decent replayers (and Amiga hardware) have a low-pass filter to cut down on the aliasing noise generated thereby.
In any case, if I'm being asked to
pay for effects I can get from Winamp, I'd have a few choice words to say about that...
