I usually stream my favorite out of town sports station and Sirius XM music stations while driving my 1999 X308. I actually bought a face plate to allow for an aftermarket single DIN head unit, but didn't want to ruin the original look of the interior. I have been using a cassette tape adapter to stream into the original radio. It was an OK solution, but I wanted an AUX jack for better sound and also in case I wanted to install a bluetooth device later since the newer iPhone don't have an audio jack. I found a site called Factory Radio Service that does this. Jaguar 98-99 XJ8 with AUX input [JA001] : Factory Radio Service, Car Factory Radio Services

 

I'm a big fan of the "hack-your-cd-changer" method, but that looks like a pretty slick solution. Reasonably priced too. Probably better to go for the external port since that faceplate mounted cable would get in the way of some of the controls.

It's a bit unclear how they set it up though - I'm guessing they hardwire that port to one of the preamp inputs and just have you switch to CD mode or whichever when you want to use it in "aux" mode, as opposed to enabling some hidden factory "aux" option.

 

A few years ago, someone was selling kits to tap into the CD changer. I ordered one and then got a reply that they were no longer available. I haven't been able to find them since.

 

The way mine works is that you have to have the radio on FM. When you plug in the Aux cord, it overrides the FM input.