So I'm trying to launch jack and, as root, I type
#jackd -d alsa -r
44100
I suggest you install qjackctl from Thac's RPM's and run it as a
normal user. It's a lot easier to tweak the JACK options that way.
Couldn't open hw:0
for 24bit samples trying 16bit instead
Try the 'force 16 bit' and 'realtime' options and set Audio: to
playback in qjackctl (click the Setup button) and most of your errors
should go away. If you still get xruns you can increase the
Frames/Period and Periods/Buffer setting.
Cheers
Daniel