I successfully configured PulseAudio to run ontop of JACK by following this surprisingly easy description.
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 seperately at once. I tried for example changing
load-module module-jackdbus-detect channels=2 in
/etc/pulse/default.pa to 4 channels - 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 use for it. If I have had an idea, I already forgot. ;-) Tell me if you know already.
Also think about my related question about JACK Audio muting Speakers but not playing through Headphones, please!