played around with Audacity (due to the fact that I discovered the jack option, but will prefer Audacious, if I could ever check it) and wanna share;
Audacity connected with Jack -> sound ok; Audacity not listed in pavucontrol
If no changes made (one runtime of a song) Audacity and MusE have both sound, until any kind of change in Audacity
so this connections seems to be right:
PortAudio in QJack is changing "out_XX" to:" out_X1" and next to: "outX2" etc. every time when change of the audio in Audacity
persistent patch in QjackCtl is active but, and what I learned here that there is the old out_XX saved
connections in this view can't be defined in more detail: