It didn't matter what I did in the mixer once jack was setup with alsa, and I had the USB interface setup in settings of qJACKctl. All I had to have checked was the main sound out
edit: Ardour handled the sound output when I turned on the monitor and piped through Jack....
edit2:alternatively one turns on the hardware monitor option in configurating the thing in setup, then route through system outputs in the connections screen, but you probably know all this, just took me this last hour to figure this out and I'd been messing with midi all day trying to get qsynth to make a sound, this is why I mentioned that iceberg... I can see the thing calving off... what a neat distro... was really pissed until a second ago till I got the hardware monitors working... lol u should have seen me, madly patching stuff through VU monitors to system:out and nothing, plus wasn't entirely sure ffado was working, I did get the metronome out of a midi hookup, but on the interface's monitor, but to stay on topic, a nice thing to have would be a volume control on the USB turntable, and they even mention this on the audacity site disclaiming all responsibility, but barring that at least now I can patch it out to an amplified system or put on headphones if I needed it loud.
you can find this comment @ http://wiki.audacityteam.org/wiki/USB_turntables
but audacity wasn't really stable with my USB Turntable, OTOH I do like it and am glad it's on this distribution for it's many other uses