Wow, I just now read up on Apple's support for A2DP. It's really sorry isn't it? Pioneer's module would allow for the receiver's remote to step through tracks, pause, and even show song titles on screen. But Apple didn't implement AVRCP at all. So you'd get play and stop.
So yeah a dock is your only hope. But it would have to have access to the file information on the player (digital), along with transmitting the raw files (codec support).
You know what you need, now it's a matter of finding if someone makes it.