Hi, I just returned to this (Csound Unity on Windows 10, SteamVR) and it appears that the simple, but inelegant workaround is to copy the dlls into the root directory of the deployed game, as a peer of the _Data directory
but I got the idea from a related suggestion https://stackoverflow.com/questions/10003028/dllnotfoundexception-in-unity3d-plugin-for-c-dll
"Well I got it working. For others who may face this problem, if you have more than one dll, you need to put the secondary dlls at root level of the Unity editor (e.g. C:\Program Files\Unity\Editor) and the actual referenced dll from script into plugins folder. This worked for me."
I would still like to find a better solution, however