Using optical, you would lose any CEC functionality, and be restricted to Dolby Digital 5.1 as the maximum codec. So no Atmos. 

For what it’s worth (likely nothing whatsoever), I’m fully disenchanted with my two Vizio TVs, both aren’t more than 3 years old, but neither will pass Dolby Digital plus from an HDMI input. They will, however, send Dolby Digital plus from their ‘Smart’ apps. When these TVs get replaced sometime soon, I’ll likely choose another manufacturer. 
 

Edit:Yes, I’m annoyed and whining. 

Ok, thanks. Vizio is going away, probably a 77” LG OLED next. Just beginning a renew of the entertainment space. 

Not quite sure you are right about eARC and 4k being on the same port, the  reason you state for not being able to connect the Firestick correctly. Reading the manual (https://cdn.vizio.com/documents/m75c1/qsg-m75c1.pdf) there’s no mention of eARC, but all HDMI ports seem to be 4k capable (either 30 or 60 fps).

Normally, audio is passed from an input device, such as a cable box, disc player, media player, or such to the TV over an HDMI connection. The TV’s speakers are terrible. Better sound can be achieved if the input devices are connected to an A/V receiver or soundbar and only video needs be sent to the TV. Now that we have TV “Apps”, we need to be able to pass audio from the TV App back to the A/V receiver.  HDMI-ARC (Audio Return Channel) and HDMI-eARC ports are designed to allow a TV to return audio to an A/V receiver or a device like the SONOS ARC. Audio travels back to the A/V receiver on a different set of pins in the HDMI cable and the A/V receiver must be designed to accept this alternate audio feed.

A TV only needs a single HDMI-ARC or HDMI-eARC port. If this port is also the only TV port that can accept 4K input there is a dilemma -- one must give up 4K or audio return. In my opinion this is a silly design, but these sets are out there. Usually these are older TV’s, built when HDMI-ARC and 4K chips  for TV’s were much more expensive.

Regardless the manual, 4k only works on the arc/earc port. For the Firestick 4k. 
 

And, received the Sonos Arc early, it doesn’t work on the arc/earc port. No sound. Low end TV, low end results. 
 

So, Firestick goes back to earc HDMI, Sonos Arc goes to optical, no Atmos. Timetable for the TV upgrade has been moved up. 

Good plan, my Firestick 4K is happy on my Sony’s first HDMI port with my Arc on the e-ARC.

I did have to make choices as I have more high definition signals than the Sony can accept so while the Firestick is being fully used my DVD player is on a slower frame-rate HDMI port.

I’ll pay more attention to the full specs of the HDMI ports on my next TV purchase!

While I applaud the sentiment, for me it was an issue that at the time of taking a decision, I was unaware that these issues might be important, in the future. To my chagrin. 

This is the dilemma. Despite tech companies talking about future proofing their equipment, generally (with the honourable exception of Sonos) this is not possible. No-one can foretell the tech innovations of 5 years hence, and as Airgetlam says, you make your decisions based on your needs at the time. I remember buying  some tech some time ago, with a feature I thought might be useful in the future (which obviously  added to the cost), which I never used. 

I agree with @106rallye  - why would a FireStick 4K require its own ‘audio return channel’ or ‘enhanced audio return channel’? - that does not make any sense.

I have a Fire TV 4K and my TV (LG C9 OLED) - like every other TV I’ve seen - has one ARC/eARC port only and that’s used by the Sonos Arc (Receiver of the returned-audio) from the playing TV source - the FireTV 4K works just fine connected to the straightforward HDMI-3 port.. I get full functionality from the Amazon product. (Display settings from my Fire TV 4K attached)

Something I’ve learned the hard way over the years is if you are mostly unfamiliar with a technology and encounter a “it doesn’t work” problem it’s down to operator error 99.99% of the time. 
 

Continued to dig around and finally determined that the HDMI port labeled in yellow is the 60Hz port, not HDMI Arc. 🤬 60Hz is HDMI 5. Arc is HDMI 1. So, I can plug the Firestick into HDMI 5 and enjoy 4K video, the Sonos Arc into HDMI 1 and get…Dolby 5.1. No Atmos. But at least I get sound. I’ll keep picking at the issue, see what comes up. 

You’ll note in my most recent post I was mis-identifying ports. Also, my Display Settings for my Fire TV match your pic. But, if I push the input button on my TV remote the resolution displayed is 1080p unless I’m using the 60Hz HDMI port, in which case the resolution displayed is 2160p. 

As the TV is HDMI-ARC only, despite its support for the compressed audio codec DD+. I would not expect to get Atmos audio on the TV - not all TV’s without (enhanced) eARC tend to support Atmos compressed audio, even though the codec/hardware are technically capable - in my own experience most TV’s with ARC don’t support Atmos but those with eARC often will. I would be happy with DD 5.1 anyway, but if wanting Atmos you could always add an audio extractor to the setup to provide Atmos audio using one of these…

HDFury Arcana

https://www.hdfury.uk/product/hdfury-arcana/

Feintech VAX04101

https://feintech.eu/en/collections/hdmi-topseller/products/feintech-vax04101-hdmi-earc-pass-switch-4x1-for-soundbar

OREI HDA-931 or OREI HDA-935

https://www.orei.com/products/dual-hdmi-earc-audio-extractor-converter-4k-60hz-18g-hdmi-2-0-arc-support-hda-931

https://www.orei.com/products/dual-hdmi-earc-audio-extractor-4k-60hz-with-optical-port-3-5mm-jack-18gbps-bandwidth-hda-935

Ezcoo

https://www.amazon.co.uk/Splitter-Soundbar-Bi-direction-Breakout-HDCP2-2/dp/B0BBZGPT6F

The above are just some examples and you may find other similar audio extractors that now support Atmos too in various online outlets, like Amazon etc.

Thanks Ken, I’ll not invest anymore time in this. DD 5.1 is good, I can back burner the OLED for now. 

Yes, that’s likely what I would choose to do too.

This is why a component based approach is often the best way to go, rather than an all in one device.   Buy devices that do one thing really well rather than doing lots of things, sometimes mediocre.  When new tech comes out for an improved function, you can replace just the component with that function, rather than an all in one device that still does others things well, except for that one function.

So you get your TV for the video quality without concern for it’s audio processing, your speaker system for the audio quality without concern for it’s video processing, whatever source you want, and one of the devices Ken listed for it’s ability to send audio and video to the right place.

Speaking of component based, I have a system for sale. 
 

Yamaha RX-A1030, Ascend L/R, center and surrounds, Boston sub. 
 

Been a component guy since forever but we are reworking the entertainment space and I just don’t want to hassle with all the re-wiring with the associated hole cutting and patching, painting etc. Not to mention my hearing ain’t what it used to be!

I’m really pleased with the Arc, gen1 sub and Sonos one surrounds for the TV. Not to mention music sounds great as well. Bonus is simplicity of use for others in the family that are even more technically challenged than me. No more “honey the system has no sound”, or “honey I can’t get a picture”. 
 

Moving ever forward…