Bonzi - you understand my idea correctly, it will support in-home and in-car tuner configurations as well as 'no tuner' configurations.

Mike: re: CD input idea
I'm not sure if your idea will work 100% as stated.

As I thought the CD pin was used for the Cellphone Mute input [which is a seperate wire on the docking sled harness].

You plan to wire the Real TX Data pin via some method to the CD pin on the Serial port/or the cellphone mute therefore allowing you to output some serial data on the serial port and check for the Cellphone mute [aka CD input] toggling in the predefined way.

However would this mean that any apps outputting serial data to the serial port [while the player is docked in the same sled] would also cause the CD pin to toggle as the data went oout and this would presumably make the player think the cellphone mute was going on and off?

Does this not effectively prevents apps using the serial port while home docked - something I thought we wanted to avoid.

Personally while the Tuner module idea is a little more complicated - it is inherently fail soft - it won't glitch anything if done right and still lets you have a Tuner module at home [which I also intend to have setup on my unit] and/or in the car.
[Simply tell the software what the ID of the Tuner module for 'home docked' is and keep the in-car and at home tuner modules Id settings seperate from each other]

However if a reliable way to use the cellphone mute in the docking station at home can be found without compromising the use of this mute setting in the car or the serial port in the home docked setting - (remember some folks may want to have this mute available in their car) then I bow to your skills
and say 'do it'.