I don't really have answers to your questions, but -

I have a 2003 S-type with the premium sound package.  I believe the premium
sound package includes upgraded speakers, a higher-end power amp, and six-CD
changer.  In the trunk, on the driver's side, there is a storage area with a
door that houses both the CD changer and the power amplifier.  The in-dash head
unit provides access to both the single in-dash CD player and the six-CD
changer in the trunk.  The question is whether or not the cars without the
premium audio are wired for it anyway, and I don't know the answer to that.  I
would tend to guess that they aren't, since this is only a factory-installed
option, but I have no idea what those wires are that you're seeing.

My guess would be, however, that a fair amount of re-wiring would be necessary,
regardless.  My advice would be to get someone at Jaguar service to answer your
questions, or find a local high-end car audio store with a pro installer to
help you.

By the way, after comparing the different systems, I decided that I had to have
an S-type with the premium audio.  The only car in my area at the time that was
in the color I wanted (British racing green), and had premium sound, ALSO had
the V8, which I didn't really need.  I got the car anyway, so I view it as a
very expensive audio system.  :)   I really enjoy it, though, and couldn't
imagine having a car without this audio system or something comparable ever
again.  It sounds 100% better than the Bose system that I had in my previous
car (an Acura).

Michael W.
Chicago, IL, USA