Hi Paul,
I have the 3rd gen with satnav but no USB connection.
Dont know if I trust myself to do the installation you have done!
Have put a call through to Lexus Service but I suspect they will charge like wounded bulls to do it.
Might just have to stick with the Aux connection and manual control.
Seems crazy however that the iPhone connects via bluetooth but iPod part of the iPhone cant work.
Regards