do you know how to connect Audacity to JACK? It doesn't show up in JACK's connection menus.
With jack started, in Audacity: Edit -> Preferences -> Devices: Select Jack Audio Connection Kit. Did you notice that JACK is an recursive acronym?
Well, this is not all. Audacity is not very jack friendly. Its ports (portaudio) appear/disappear when you press/unpress the play button. Use the pause button as a workaround. For example, to record: Press Record, then press pause, make jack audio connections and finally unpress pause.
I am glad I helped.