Your ~/.jackdrc should look like this:
/usr/local/bin/jackd -Z -R -t5000 -dcoreaudio
I just discovered something I wish I hadn't: It seems that jack_open_client() will FAIL for some .jackdrc files which contain valid command lines. UGH.
It's unclearly exactly WHY this is, but I'm so not inclined to find out at the moment.
I wonder if LGL_JackInit() should write a good ~/.jackdrc if the file doesn't exist... I'm tempted to say "yes", if only because the alternative is to allow our user to fail initializing JACK.
-Chris