Final solution: Returning the JT160 to Amazon - may have issues with not returning it in the original box, but I'll deal with that later - so far they say no problem. And ordered the Bridgewood from Wilke's. I suspect I would have no more luck than Tony. I called the local Delta service today and they were as helpful as they could be. I told them I suspected a slightly warped outfeed table and they put in an order to ship me a replacement - and they mentioned that the infeed and outfeed tables were identical - something that's pretty obvious when you look at it, but I didn't notice anyway. So I scampered downstairs and swaped them and gave it a try - but no joy, I had exactly the same problem. Then I loosened the nuts that hold the plates that the tables mount onto (thinking that maybe one was bound in an unlevel position. When I measured it, it looked like I had fixed the problem.
But I ran a couple of pieces through and got exactly the same results. I said "gosh darn" and got on the phone and ordered the Bridgewood.