Firestick 4K and Sonos Arc both require an eArc HDMI port, only have 1

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.