I'd hoped that this version of the boards (above) would be the final 'release' version. There are some very minor tweaks to make but I'll be building 5 of these - one for myself and four for people interested in an 'earlybird' deal. I'll try a black version too.
The firmware has taken many many hours, and it's clear that there will always be new features on the horizon. If it sells then I look forward to the ongoing development.
It's working very well, see the video below, in which it is in 'General MIDI' mode, I'm playing in the MIDI files for the DOOM levels.