So, I'm not having a lot of trouble with NixOS per se. But NixOS kind of prescribes jackdbus w/pulseaudio, which I've never done; I've always just used jack1 and killed pulseaudio. I roughly followed this (roughly, because, among other problems, the qjackctl version is quite different): https://nixos.wiki/wiki/JACK
. I managed to get ardour5 working, but *most* jack clients fail to connect. Ardour is *extremely* unstable too, but I defer that question to avoid muddying already murky waters.
Maybe you could start by describing, at a high level, how you're running things.
Pulseaudio has always been a thorn in my side, too, honestly. I work around it by letting it have the onboard audio by default, and mostly use Jack in combination with the outboard interface. I'm on a laptop at the moment, though, so YMMV.
Physical setup: Dell XPS13 with Mackie Producer 2.2 interface via USB, plus the usual rat's nest of audio and MIDI cables - I'm actually round-tripping the MIDI through a BeatBuddy, then through an Amplifire, and back to the interface. Oh, and the Mackie comes in via a USB bus, because I ran out of sockets on the XPS (also because I'm lazy, and I'd rather plug/unplug 1 cable than 3).
Jack's been pretty solid for me; the biggest problem I've had lately has been that it typically doesn't exit with qjackctl, causing a few WTFs until I spotted the pattern. Ardour's been good as well, so our experiences are very different at the moment.
I'll post my Nixos configs tonight, when I'm at my personal machine and have ready access to them. One of the nice things about that OS is that it's about as deterministic as it gets, so comparing configs can get you a pretty long way.
Is there a pattern to the kind of thing that causes Ardour to crash for you? Maybe a pattern in the logs/messages it leaves behind? Similarly, is there a common message in the qjackctl messages panel when things fail to connect, assuming you're using that to manage it?
I'm slow, but I get there eventually.