I looked at the Harman Kardon unit, but not very sure at all that it'd be compatible with the HU's in our cars....
From what I can recall from memory, that needs an aerial in port to hook up to the HU, and I can't see one on the back of our units....
They do a Harman Kardon Wireless version of the Drive & Play, but then you're just getting back into the realms of iTrips and the like......
I particularly liked it at first for it's Blue screen which would fit nicely with ours, and the scroll wheel thingy reminds me of BMW's iDrive system...