The assembly was upgraded, any idea if it's backwards compatible?

 

No there is totally different transmission software between the 4.2 and 5.0 cars

 

I figured as much, shame. My chrome has chips and there's a bit of wear on the knob, but a new one is $400. I figured if I was going to be spending that much, maybe look for a nicer one.

 

This. British Autowood > Gearknobs

 

Is it purely a software issue? I understand that early 5.0 X150s still had the 6HP26 box as fitted to the 4.2s, I did find myself wondering what the stumbling block would be...

 

I don't see why it would be a software issue. The shifter, whether a rotary knob or linear rod, operates switches that tell the software what is selected. I have never had either one apart, but if you can get at the switch contacts you should be able to wire them to the software/hardware interface to accept the input from either shifter. Both shifters have five positions and switches - P, R, N,D, and S. The software does not care how or what actuated the switches.

Someone that has them apart can comment if the switch contacts are accessible or burried in a CANBUS controller.

It might take a little work to make the rotary knob retract when shutting the car off.

 

It seems to me that during my search for a 2007-ish XK I ran across someone who had bought but not installed the knob type shifter to replace his stick-style shifter, and he was including it in the sale. That doesn't necessarily mean that the switch could be accomplished, but I guess he thought so.

 

It'd be easier and cheaper to sell the 2008 and buy a 2012 (or any 2010+). Plus, you'd get all the added goodies to go with it.

 

+1