I posted this over at the Ardour forum as well, but every time I post over there they just tell me I shouldn't use Ardour/Jack with Slackware...
I installed the libffado from Slackbuilds.org yesterday on my -current box, and followed the instructions in the README for configuration. After I did that jack wouldn't start at all, insisting that there were no recognized drivers, even when I had the alsa driver selected (alsa is working fine, by the way... I have sound). After doing some more research I uninstalled jack and built Jack2 (1.9.6) from source with the following configure options:
./waf configure --firewire --alsa --dbus --enable-pkg-config-dbus-service-dir
Now when I try to launch jack (regardless of selected driver) I get the following message in qjackctl:
21:05:32.183 JACK is starting...
21:05:32.183 /usr/local/bin/jackd --no-realtime -r -dalsa -dhw:0 -r48000 -p1024 -n3
21:05:32.185 JACK was started with PID=30359.
Unknown driver "alsa"
Copyright 2001-2005 Paul Davis and others.
Copyright 2004-2010 Grame.
jackdmp comes with ABSOLUTELY NO WARRANTY
This is free software, and you are welcome to redistribute it
under certain conditions; see the file COPYING for details
21:05:32.191 JACK was stopped with exit status=255.