Surround on L/R Stereo Setup

Hello, I hope somebody can give me a hand with this:

In my project, we want to work with some AmbiX Files for special places. We plan to use the Resonance Audio Plugins for it.

The question now is, how does the output format for FMOD look like. (There are multiple questions. I will give numbers, so you can better answer)

The AmbiX Files are 4 Channel files. They go into the RA sound field plugin and route to the RA Listener Plugin in a separate bus before going to the master bus. That’s because I still use mostly regular audio files.
My physical setup is L/R Stereo. The RA Listener gives an L/R Stereo output; I guess that is always the case because it is meant to be for headphones, right? Would that change, if I had physical 5.1? (1)

However, the game is not made only for headphones, but for people with L/R, Surround, and HP devices. Does it make sense to set the Subgroup or bus, where the RA Listener is located to a 5.1 output, to give a surround signal for the surround devices? (2)
Means, I could tell FMOD to still distribute the L/R output (form RA Listener) to HL and HR as 5.1 (that’s with attenuation for surround etc, center and sub get nothing!), but no idea if that really makes sense!?

What happens internally, if I say to FMOD and the Engine that my setup is 5.1 surround, but my physical output setup is just L/R Stereo? (3)
Do they get mixed or do the surround channels simply run into nothing?

I hope I worded it understandable.

You can change the channel format of individual events in FMOD Studio by right clicking on it’s Out meter in the deck and selecting the desired format. Leaving it to the default of “Automatic” results in the channel format matching the content of the track- adding a 5.1 audio file will make that track 5.1, Stereo will make it Stereo. Please see the Changing Channel Formats section of the docs for more information.

Yes it does make sense to set it to 5.1 for compatibility with surround outputs, and rely on downmixing behaviour (see below) to map to stereo. If you are targeting multiple formats then you could alternatively set Platform specific channel formats for your banks. More information is available here: Compression Formats and Platform Settings.

Internally FMOD maps whatever inputs it is given to whatever output is available. In the case of Stereo->5.1, the L and R channels will be mapped to FL and FR respectively, and every other output will be silent.
In the case of 5.1->Stereo, then a weighted sum of the FL, C and BL channels will be directed to the L output, and FR, C, and BR will likewise be mixed down to the R output. Note that the LFE will be lost in this downmix. You can read about FMOD’s default Upmix/Downmix behavior in the Upmix/Downmix Behavior section of the Core API guide.