I don't think you should see anything in aplay because aplay is ALSA specific, and FFADO does not yet work with ALSA.
After setting the JACK settings in qjackctl, you have to start the jack audio server by pressing the start button in qjackctl. If it is running properly, qjackctl will give some cpu percentage statistics in its main window. You can also open the messages window to see what is happening.
I've attached a screen grab of the settings in qjackctl for firewire. If you are not running a realtime kernel uncheck the realtime setting.
The following command line will also start jackd, and any error message should be printed out to the console window if it fails, if you don't want to use qjackctl.
jackd -R -d firewire -r 44100 &
Under jack, the same user that starts jackd also has to start the audio app that is accessing jack. So, if jackd starts properly, try something that definitely supports the jack output, like aqualung, but you have to specifically set the aqualung settings to use the jack output. MPD also has a jack output, so I'd be happy to pass along a configuration for that once you get it working with aqualung.
ALan
