JuceOPLVSTi VS fat1.lv2

Check this out https://github.com/bsutherland/JuceOPLVSTi

A workaround is to not use OpenMPT's built-in OPL samples, but instead, an OPL VST instrument plugin like JuceOPLVSTi, and make your OPL instrument use this plugin instead of the OPL samples. Then you can either apply the reverb plugin to the channel you want, or just route the output of the OPL plugin to the reverb plugin.

JuceOPL — a clean FM/additive synthesizer.

I don't think the Volca FM would be a good choice for that. For a start, it can only play one instrument at a time (no drums/bass/chords playing alongside the melody). The sequencer is only 1 track and 16 steps. If you want to spend some of your time instead of money, you could try getting more acquainted with Ableton of FL Studio and use a free VST like JuceOPLVSTi.

I ended up using https://bsutherland.github.io/JuceOPLVSTi/ since it made composition way easier than messing around with tracker software. I haven't really looked into extracting the patches from the game, but i'm sure it's possible - it did have a jukebox mode after all.

X42-autotune here

Plugins don't make good music. That's what artists do. And there are alternatives to Warez...

x42 Auto Tune — my go-to autotune plugin, modelled on Zita's AT1. Very barebones, with tuning/bias/correction/speed controls, you can select which of the 12 chromatic notes to retune to, or you can also sidechain to a MIDI channel to force tuning to a particular note in realtime.

Fons Adriaensen's zita-at1 is supposed to have really good quality pitch correction, maybe worth a look? Here's Robin Gareus's fork on github for easy browsing. It's GPL though so I don't think you can copy-paste it into an MIT licensed project.