Link Star H68K is, according to multiple sources, exactly the same as Hinlink H68K.
But that's not the problem (yet).
I'd been using an old version of RKDevTool (2.84 IIRC) which was unable to load the .img file from the Armbian site, but uninformative as to the nature of the problem.
Updating to RKDevTool 3.37 at least yielded an error message when attempting to load the image:
Googling this suggests a corrupted download (not the problem here, the SHA sum matches) or a raw .img format rather than the packed .img format expected by RKDevTool.
So I compiled an image according to the Armbian Build Framework instructions. Same error message.
More Googling suggests that a couple of Linux CLI utilities, upgrade_tool or rkdeveloptool, may be able to flash a raw image to the board's EMMC.
More later...