I have the 8 channel filter working (only needed six here). I think it sounds awesome, resonance is quite picky though. It can be tamed by the trimpots but when you are on the edges it produces some pretty funky sounds. Cutoff frequency is also controlled by LFO and/or ADSR.
I fixed some problems on the MIDI implementation of the DCO, also USB MIDI seems to work now. There has been an update of the Raspberry Pi Pico SDK and it now uses upstream copy of TinyUSB.
I think I got a proper polysynth now! Okay, it’s quite basic and I’m still missing some casing but it works.