The vendor got back to me. They provided Windows drivers, the PC software and a neat little docx file that "documented" the protocol. Winner.
When I get a moment I'll post them somewhere. The archive is ~250MB. Haven't even bothered to install the software, just knocked up a bit of python to control the supply.
For a fully controllable 30V/10A PSU for less than $150 landed, I'm quite impressed.