Some time back when I was going through the trauma of trying to sort out this problem and the confusion about frequencies etc, I thought seriously about abandoning the Jaguar system altogether and installing another system to replace it.
Firstly, I don't think it's as easy as just unplugging one unit and plugging in another of a different make!
Wiring systems in cars are very complicated things and vary, not only between makes and models but also between different years and models of the same car!
Replacing the system would firstly need the correct wiring diagram for the car in question (as I said before the same basic model can have different wiring diagrams). Next, someone with auto electrician expertise willing and able to tackle this job.
All fine if you are capable of doing all this yourself, then I say good luck and report your experiences. But if you've got to pay someone to do this, coupled with buying the new system then surely it can't be more economical than fixing the existing Jaguar one?
Or can it?

 

*HELP* how can I tell which key fob I need, is it the 315mhz or the 433mhz 1996 VP XJ6

 

Look at the top center of your rear windscreen. Look where the two short security antennas come out of the square patch.

If one goes out the right side and one out the bottom, you have a 315 MHz system.

If they both go out the bottom of the patch and split, you have a 433 MHz system.

315 MHz = DBC11510 remote
433 MHz = DBC11512 remote

Cheers,