Ok, I deffo don't want FM Modulator now....
With the radio on, a neighbour of mine suggested pressing and holding CD button for a couple of seconds. I did, and AUX came on info screen, so I know there's a facility for it. So, I took off the gearstick panel and the radio/CD panel. Thanks for that heads-up.
The head unit is a Mitsubishi Electric DY-1ME8U4-T, s/n 8701A117. I answered at least one query I had by looking at the back of the unit - although there is a factory option for a 10-disc CD autochanger on my Elegance model (standard on the Warrior model in UK), it hasn't been taken up. But there is an empty 13-pin aux port. So I can do 13-pin DIN to headphone jack for starters...or, l need is something like this, I guess: