I thought this topic warranted its own post.
Success! I tried a KDC-X993 (which I am now the proud owner of) with my VW Phatbox through a KCA-S220A switch, and it worked perfectly. HDD EXT is the displayed source option.
Actually a quite interesting afternoon. I went to Radioactive in Burlington, ON, for some spade lugs, and thought I'd see if they would let me try hooking up a lower end 2009 KW deck, just to see if it worked with the PB. I went armed with my correspondence with the KW Canada tech. I had just read the deck I was waiting for (X993) was delayed until April, and I was tired of waiting to find out if I was going to keep my current deck (A 2007 X791, which I never really liked and was never really installed permanently) or if I could get a 2009 deck. So I started to explain how I wanted to test the compatibility, but was waiting for an x993 and... it turns out the store had just rec'd them days before, and he would let me try it out, and if it didn't work, I need not buy it. He also offered me a pretty good price. We took it to my car, plugged it in and voila, success!
Since the deck has no dedicated scan button, it is a few more key presses. First the FCN button, then presses of the main selector knob lets you cycle through genre, artist, album, etc. Then a press of the FCN button again. But you get to stay in the selected mode, so let's say you are in artist mode: up/down toggles of the main selector now bring you up/down through the artist list, left/right of the main selector switch tracks, and double left/double right lets you move through the alphabet. Quite different from my VW stock radio, where you had a limited time to make a selection and then it would switch back to track mode.
If someone tries a 2008 deck through the KCA-S220A, I'd be curious to know if that works too. I may also try the X993 without the S220A switch, but I doubt it will work as the information I got was that the S220A had to be used for PB compatibility. Of course 2007 and earlier decks work directly w/o the S220A.
Cheers,
Jeff
Update: I contacted KW support about 2010 decks, and they confirmed with Japan that 2010 models will not support the music keg/Phatbox, so stock up on compatible decks before they are all gone!
Update:per post below, seems that info may be incorrect, and 2010 decks will work - stay tuned...
Update: I tried a 2010 KDC-X994 (with S220A switch) and it works - see reply 15 for details.
Update: I tried to sum everything up in reply 17.