Help with WinVICE and ZoomFloppy

[LoadError]

I recently rebuilt my home system, switching from Windows 7 x64 to Windows 10 x64.
I have installed my ZoomFloppy interface and the companion OpenCBM tools following this tutorial: https://opencbm.trikaliotis.net/opencbm-8.html
I can now use the interface via command line (directly invoking the OpenCBM tools) and with CBM-Transfer (the latter required copying some missing OpenCBM files in the program folder, in x86 flavor since CBM-Transfer is 32 bit).
I am unable to make the interface work in WinVICE.
I used to be able to load programs from the actual 1541 drive via the ZoomFloppy interface by setting up drive 8 as "Real IEC" in the VICE settings, but this was with WinVICE 3.1 (x64). Now I am using GTK3VICE-3.3-win32-r35896 (as there are no x64 builds other than experimental ones), downloaded from https://vice.pokefinder.org/.
I have enabled the "IEC Device" option in Peripherals - Drive settings - Drive 8, but when I try to load a program the 1541 does not react and VICE throws a "file not found" error.
OpenCBM v4.99.99 is installed in C:\Program Files\opencbm, and this path is included in the %PATH% environment variable, so any app that directly calls an opencbm executable can "find" it. But this goes for x64 apps. Since VICE 3.3 is x86, do I have to (also) make a C:\Program Files (x86)\opencbm directory with the x86 version of opencbm, and then add this to %PATH%, so that VICE can "find" it and finally enable the "Real IEC device" option that is currently not even greyed out, but missing altogether from the GUI? And possibly this would avoid having to copy single required x86 OpenCBM tools in the CBM-Transfer directory?
Or maybe WinVICE 3.3 is no longer compatible with the ZoomFloppy?

[LoadError]

I'm going to answer myself.
It's not an issue with x32 or x64 or with the system paths; it's just that the version of WinVICE I was testing just does not have the "use real IEC drive" option. I found it on later experimental builds, but those have issues of their own, so I will just revert to version 3.1 which I was using before, and which has no problems.

[LoadError]

I'm trying the freshly released nightly build GTK3VICE-3.3-win64-r37084.
It has the "Real device (OpenCBM)" option, but it won't work.
The console window shows this error:
"USB release intf error: libusb0-dll:err [release interface] could not release interface 0, win error: The required resource is in use."
This happens in xvic.exe, but oddly enough, does not happen in x64sc.exe, which works fine...