" It's only functions will be play all and volume control."
I understand, but I don't understand.
Play all what? Playlists? Just start playing all of my 10000 tracks without regard to what it is? Most people would need some sort of feedback so they could pick album/track/playlist/genre/etc.
"You then could select the next track by pressing the button and turning the knob."
Again, this is not practical if you have multiple albums to choose from. How do you know what album you're playing? One of the most important features of the music module is the "Search" feature. This can't be used in this Powermate setup. How many albums and/or tracks are in your music library? What if you want to play an internet radio station? How do you choose a station? How do you even navigate to the Internet Radio section without seeing where you are going?
I just don't see how this type of control would be useful unless all you wanted to do was play the same music playlist (likely on random ) everytime you started your music player.
IMHO, a solo Powermate control knob system without some sort of visual feedback seems way too limited to have broad appeal.
Not to completly rain on your parade, I did a search and found this for ya.
http://www.keyspan.com/products/usb/server/ (I could also probably use one of these babies!!)
hjackson