Also, depending on how you installed it you may not
have compiled in
JACK support?
Just installed it from the debian unstable repo
You may want to check whether it is JACK enabled. I've only ever used
the debian derivative Ubuntu, and I'm not sure whether they also have
that ridiculous "cannot link to apps in different repos" rule that
prevented JACK support for some apps.
I just checked; I installed mine from the Debian Multimedia repo, not
the vanilla Debian. I'm also using the Rivendell repos for Jack, it's a
very good place to find a very stable, reliable, repo-aware Jackd.
J.E.B.