Dead chuffed that I managed to get this sucker working (in the end)!
Based on the ARMSID SID replacement chip, with an Arduino Uno handling the USB, MIDI and chip-controlling bits.
Also includes an FLStudio dashboard to control it with and enable saving presets etc. Flashed the bootloader with USBMidiKliK to make it appear as a class-compliant MIDI device and now I can just plug it in to USB and my default FL template has the generator all set up and ready to go with a preset loaded ready to start tweaking and recording!
Code over on github, featuring an adaptation of Notes and Volts‘ LFO to enable LFO modulation of filter cutoff and pulse width. Forked from ‘therealjaypo’ SIDI which appears to be unmaintained and I haven’t heard back from the author. There are some blog posts over at http://hatestheinternet.com/kraslophone/midi-sid-arduino/sidi [although the site seems to be down as of 2020-05-11]