Does anyone know something about the synthesizer program they are using? I saw it is not yet published, but I wasn't sure if there was some information about what type of synthesis it was using or what the processing chain was like.
That may be unlikely, considering a few of the things you mentioned are proprietary or not available for OpenBSD. What is more likely is that Alexandre created something new, which makes sense considering he also created the sndio API discussed in the article.
Is OpenBSD well suited for realtime synthesis? I've been looking for a minimal platform (no graphics) with better latency than linux out of the box, to use with SuperCollider and puredata.