Success with Raspberry Pi 5

Many thanks Skabadee,
I'll certainly use your findings if I finally get opportunity pick up this project again.

The SequencerWrite indeed exists & works in the original version. If you don't use the smfplayer (which is a quite niche thing indeed) it doesn't matter.

sounds.py: looks OK to me and if your samplerbox does work as expected (= sustain/loop sounds when holding down the key - which is controlled by the changed code), the ChatGPT also did some nice work by formatting this old code into a more readable version  

rtmidi.pyx: one serious change there, this will need testing. But if it works, also in improvement in readability..

But I'm happy that the critical/complex pieces of code survived the upgrade. The python2.7 => python3 conversion (needed for PI4) came with more serious headaches 

Thanks again, Hans