Update: success! Got it working, thanks to the advice in the "Ultimate Guide to installing Roland Drivers" forum posting.
1) I installed the driver by clicking on Setup in the 64 bit folder for the driver package, it launched, said installation failed and it must be uninstalled. But when the "Do you want to uninstall the driver?" box came up, I just closed it without actually uninstalling. Checked the system, and the console was now showing up as "VS-700C" under Device Manager, although the computer didn't know what device to classify it as. Still, this was progress -- previously, the computer was identifying it as a UM-1.
2) I went into the folder with the 64 bit driver, and in the Files folder, I right clicked on the "RDIF1088" Setup information file. Chose "Install" from the context menu. I had previously disabled driver signature enforcement through the start-up menu, and so Windows now gave me its slightly panicked "Are you sure you want to install this driver, it could be eeeevil" message, and I said yes.
3) And presto! Done.
Launched Sonar Platinum, and found the console appearing in the Devices section under Preferences, made sure it was selected and set as the control surface. Tested it and everything is working fine.
Some notes:
1) When I first tried to install the driver file directly from the context menu, I was told by Windows "The hash for the file is not present in the specified catalog file. The file is likely corrupt or the victim of tampering." I had to restart, disable driver signature enforcement from the "Change Advanced Start-Up Settings" found on the start-up screen. For whatever reason, the BCEDIT method didn't seem to do it.
2) I did open the RDIF1088 file and make the usual replacements, by inserting NTamd64.10 where appropriate.
It's all working. Thanks to all the folks who have posted on this topic. Between the many informative posts and my own tinkering, I managed to get it going. I hope others find my experience helpful.
Rob