A small update - and apologies to Dynamix - their optical HDMI cable works fine for 3D
With the splitter in line from the receiver output, connecting to the HDMI 1.4 input on the projector, the Dynamix cable works fine in 3D.
When connecting directly from the receiver to the projector, neither cable works in 3D mode.
This may be similar to the issue I had when originally connecting the Vero directly to the projector that it would only cause the projector to switch to 3D mode when I enabled HDP lock, or after I installed the splitter.
This means that my projector is the issue, when connected directly to either the Vero or the receiver something weird is happening when it switches to 3D and I lose signal.
Installing the between the projector and either source fixes the issue.
My 3D Blu-ray player can be connected directly to the projector and works fine, but not via the receiver which needs the splitter between its output and the projector to work.
Neither cable will enable 3D on the HDMI 2.0 input, and I get the top/bottom display.
There are still some issues with the splitter blocking 3D mode in some EDID settings, but I am overriding that with disp_cap_3d anyway.
In any case, I need to use the second projector input for 3D so what I have in place now does everything I want.