A simple HDMI switch often comes with an optical output. You’d need another HDMI cable as well. 

Things get much more complicated if this HDMI port is an ARC or eARC HDMI output.

It actually is hdmi-arc. Would this be the problem?

and is there a solution?

That means the HDMI cable is sending out audio on a different set of pins than it comes in on, which makes things more challenging, and expensive, to my knowledge. You’d need another HDMI ARC to optical converter, something which isn’t standard with a normal HDMI switch.

The ones I’m familiar with are the HD Fury Arcana, the Feintech VAX04101k, and the OREI HDA-935. You can also order from those links from the companies directly, or check your local retailers for availability. Amazon may carry some, depending on location. At this point, there may be more manufacturers, I haven’t been keeping track.

On the other hand, I’ve not really investigated any optical outputs on these devices. 

Since the Ray doesn’t do Dolby Atmos, I’d be awfully tempted to pull off the audio using a standard switch before the signal reaches the projector, and not after. Much less expensive, and you don’t need to worry about ARC stuff. 

You are probably better off getting a Beam, or doing as ​@Airgetlam says, extracting the audio with an HDMI to optical extractor before it reaches the projector. 

I just agree… take the Beam or if you already have the Ray, take a HDMI switch with audioextractor to toslink output. 
These are the only options. For converting HDMI ARC audio to toslink I don’t know any device that would do that. 

Doesn’t one of the devices I linked to have an optical output? Not Atmos, certainly, and way too expensive, but wasn’t trying to force my judgements on the OP.

Sorry Bruce… no optical out on these devices. All of them are made to support atmos trueHD on setups where the tv can’t do so. So no need of optical connection. Would be like a Porsche 911 with tow-bar.

Thank you for your feedback! So this means there is no solution at this moment With the beamer and the ray i have?

The Sonos optical adapter is, according to https://www.sonos.com/en-us/shop/optical-audio-adapter, only “Compatible with Sonos Arc, Amp, and Beam”. It works from optical to HDMI. You need something that works the other way round.

As mentioned above you can use a hdmi switch with audioextractor to toslink (optical) option. 
You will have to connect your source devices via hdmi directly to the switch input ports. Ray can be connected via toslink to the switch. The beamer can be connected to the hdmi out of the switch.
 

I took a look at your beamers tech specs on the net and it seems just to have a single standard hdmi input without arc support.

it actually has ARC support.
I already tried with a convertor but this also did not work; is there anyone who could recommend me a (cheap) working convertor?

Thank you so much!

Ok… maybe there are different versions of the beamer available. Nevertheless… which „converter“ exactly did you try? 

You don’t need a „converter“… you need a hdmi audioextractor !!! (with optical audio output)

How many HDMI in ports does your beamer have? Depending on that and on the question if one supports hdmi arc with passthrough, you will need a simple hdmi audioextractor with optical audio out and just an hdmi arc output, or you will need an audioextractor with hdmi switch functionality, multiple hdmi inputs and one normal hdmi output. 
 

EDIT: a picture is more than 1000 words…
 

​@StephenCop 

Here two examples I found on Amazon DE…

Alt. 1 manufacturer „FeinTech“

Alt. 2 manufacturer „SpeaKa“