Now I wonder if there is a way (at first I was certain of it) to have multiple sinks between JACK and PulseAudio, for example, to record two PulseAudio applications separately at once. I tried for example changing load-module module-jack bus-detect channels=2 in /etc/pulse/default.pa to 4 channels - auto clicker but then PulseAudio won't even start.
Also, I'd really like to use this feature to reduce the volume of the JACK output before playback because I don't want to blow my ears. I also thought of creating virtual streams in PulseAudio and I may try to figure that out next, though I don't know wether I will find a use for it. If I have had an idea, I already forgot.
Tell me if you know already. Can you please describe how you configured jack, or how you want to configure jack. Not really sure what PulseAudio has to do with it. Jack can run w or w/o pulse and it is not clear what you are doing with either jack or pulse.