Hi there,
Here is the answer I gave to a user who asked me a similar question through a private message. Just my own experience.
Since VPX 10.7, I have had problems with directb2s files in VR. This seems to arise because we use 2 programs, Visual Pinball and the B2S Backglass Server, and each one wants to be on top on the display. This creates conflicts, from my experience sometimes it works and sometimes not.
Many people on the forum seem to have a separate display for the backglass. In this case of course everything is working as expected. I only have 1 display and a VR headset, and the only solution I found to see the backglass in VR on some tables is to use .res files. I put in the tables folder a file with the extension .res, and the same name than the .vpx and .directb2s files. These are the first 7 lines in my .res files:
1920
1080
640
480
1
0
0
The first and second lines are the resolution of my display, the 3d and 4th lines are the size for the backglass on the display, the 5th line is the number of the display, and the 6th and the 7th lines are the XY position of the backglass, hence in the top left corner.
What this file does is making the backglass smaller on the display, and put it out of the way so that it can get captured in VR. I tried to resize it to a very small size, and this does not seem to affect the quality of the image in VR, so that I found this solution acceptable.
For playing in VR I use the VR launcher with 3 different settings (in the config file). For some tables in my collection I have to use VPX 10.6 to get a backglas, other tables only work well in 10.7.1 (Pistol Poker), others in 10.7.2, and then the newest tables in 10.8. Of course this is a complete mess, but I can play all the tables with a backglas.
I hope I could be of any help. Cheers.