In order to have your master keyboard pluggable in Jackd, you have to install the following daemon that will perform a bridge between the ALSA driver and the Jackd server.
sudo apt-get install a2jmidid # start the gateway a2jmidid -j default
Now you can see your MIDI input « a2j » in the MIDI tab and you can plug it to wathever instrument in Ardour you want.
alboletono 