Thanks very much for the reply and the links.
Unfortunately, I think this type of programming is a little beyond me, because I would have no idea where to insert this code or how to, for example, tell it to sort by dd_priority first (ascending), then date (newest first), then alphabetically by post_name (ascending).
By any chance is it either easy to spell out, or do you have any demonstrations anywhere so I can see someone implement something similar to this?