[Jackaudio] no audio through headphone jack

Hiya, My use case is this: I have a desktop with Arch, I play music on it using the desktop audio port at the back during the day, and at night I use headphones connected to a tiny USB sound card. This works with pulseaudio, but despite being a simple scenario pulseaudio is a bit flaky and sometimes hangs. So I went looking for an alternative solution. I know that Jack is for professional audio, not some basic home use, however I gave it a try. I used the instructions in the Arch and Jack wikis. I am using jack2 with Cadence and set up a bridge for pulseaudio to Jack. Some of players that I use have Jack outputs so I use it on them, example, Vlc, Audacious, Mixxx. For Firefox and other players without a Jack output I use the pulseaudio bridge. I have been using this for a day only and so far I am happy, it seems more reliable than pulseaudio. I do have to stop the jack server and the pulse audio bridge before suspending the computer, but that is fine with me (incidentally this suspending seems to trigger pulseaudio flakiness when not using jack). The sound quality seems better with Jack – not really surprising as it is professional audio! There is something I have not figured out. If I plug headphones on the 3.5 mm headphone port in the front of the desktop, the sound out of the back to the speakers stops, as normal in pulseaudio, however I don't get any sound on the headphones. I could not find in Cadence any port specific for the headphones. Another guy reported the same a few days ago on the Arch forum so it is not just me. Is there a solution for this?