maybe the new years eve drunk was still on me but today I've followed the instructions listed here http://www.runeaudio.com/forum/rune-support-for-digi-pro-t4065.html
and added the folowing line in command.txt:
after the line where you include the Hifiberry digi.
just a quick reboot and TADAAAA!!! on the MPD list I can see the correct Audio Interface.
now I have only to take the PI from the kitchen table where I'm working and put on my stereo to make some test.
Thank to you all.
Mandi e Grazie (thanks and see you soon)