I think I solved it. Just exporting the foreground PSR dng from lightroom, and hence avoiding the development of the entire file, and combining the image as I had before, has seemed to have eliminated the moire like lines in the sky. Somebody more knowledgeable in the mathematics than I am could probably expalin why this happens, but there is clear conflict when adding a 'bayer' pixel pattern sky into a 'debayered' pixel shift resolution foreground. The export must get confused on what to do, seeing two different types of pixels.
And thanks @Adam for the link to the K70 thread, it was a good read and will look into turning on the AA filter to weak when doing an astro-traced shot. Might help with the colours. As soon as the upload to flickr is done, I'll post it for all to see.
---------- Post added 08-14-2016 at 06:13 PM ----------
Here it is. Seems much better. Now I can finish editing. I'm going to go on over to the Affinity Forum and ask about this I think, see what they have to say. I'd be interested in knowing if Photoshop would treat the files the same way. Now that I think of it, this may be why Affinity was giving me an error when i would try and save some projects: "There are no pixel elements in this project. Flatten the document and save anyway?"; this error would only pop up with a PSR file.
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