FWIW, its all done now -harness and advice from Dave (SVXDC), and a fair bit of sweat, tears and curses. All difficulties were physical R&R , no electrical issues.
After finding the HU had 4 line outs, I could have run these to the Mc connector, if we had one to match, and knew the pin outs. Hard part was getting the new cableing under the carpet down under pax seat - had to remove the seat in the end. I tried to fit an iPOD adapter, but there was such an excess of cabling with it I gave up on trying to fit it all in behind the HU.The tunnel cover was a bit of an issue, as releasing the main wiring plug was a bugger with it clipped to the cover, and then there was an air duct screwed to the cover such that you couldnt reach the aux in plug , and I had to remove the duct first - a few acrobatics required. I have left the Mc cabling in place - got no idea where it runs,dont even want to think about it. BTW, the single din cubby is 66128ae000, from Japanparts.
This is the dual zone ac version also.
And as hoped, sound is better already. All I have to do now is get a small amp to drive the Sub, and its done.
Thanks Dave.
Update for Dave - the aerial input to the Mc HU is 2 round pins, in a plug ~1/2" dia
jp 08 gtb 6,t wagon

