Sonos Arc - Getting Dolby Digital

What models the TV? Sounds like a possible handshake issue from the cube to the TV. You could try a power injector on the it and see if it fixes it but will require a USB port on the TV.  LINDY 41080 HDMI Power Injector Inserter Cable, not too expensive. 

Te model is a samsung un65f7100. It does have USB ports. Not sure what a power injector is, but I'll look into it. Also will maybe borrow a Roku from my buddy and see if the same issue follows. I really appreciate you taking the time to respond.

It's usually only needed for active cables which will have like a marker on each end to show which end of the cable needs to go where as it's not bi-directional and it draws power from the device. So the power injector gives it the extra boost when it sometimes can't draw enough power. Standard passive HDMI cables don't really require it, but oddly seen a few that adding the injector spring it into life if there's handshake issues (no idea why though). 

Just realized also if I unplug the HDMI cable going from the Fire Cube to the TV and replug it back in it also kicks it into Dolby Digital without having to restart the Fire Cube.

Yeah definitely sounds like a handshake issue then. Any ideas what type of HDMI cable it is and how long it is ?

It's a 2 footer but honestly I'm not at home now and do t remember the brand. Like I said, I did swap it out from the original one that was on there. It got the same results. When the Arcana arrives I plan on swapping all the HDMI cables out. You have any suggestions on brands for that without breaking the bank!

The TV and ARC are having an EDID spat. With a user supplied external switch, this device will allow you to switch a pin in the HDMI cable that will prompt the same EDID re-negotiation that your unplug/plug maneuver is performing now. It is slightly more convenient because you will not need to be digging for cables. Sometimes one box is too slow responding, causing the other box to fall back to a default. I have no experience with this box, but it might also solve the issue by holding the EDID constant as far as the box at each end of the cable is concerned and this box will respond rapidly.

Full disclosure: I don’t have any experience with the Fire TV Cube. Before trying the above, check to see if there is a Fire TV Cube option to specifically set the audio output, rather than depending on “Automatic”.

As it's not massive run you don't need fibre optic one, so any basic one will do. Just get cheapy Amazon basic cable will be up for the job. 

From a possible fix point of view, you could add one of these to the mix:

https://www.amazon.com/dp/B06WV5YJ6H?pd_rd_i=B06WV5YJ6H&pd_rd_w=gdRW3&pf_rd_p=5a4c43eb-7872-4818-a785-e153f6c73149&pd_rd_wg=7D7B9&pf_rd_r=WCP7R1W263RRVSQSP0RB&pd_rd_r=f3d1f417-3846-4638-a80c-3aacf5d0d678

Otherwise if you can return the cube I'd suggest doing so and replace with an Nvidia shield, much better device personally, otherwise test the above and if no luck just send back. 

Looking at the switcher it states HDMI 2.0, so I am assuming. It will pass through Dolby Atmos for when the Arcana finally arrives, correct? I also did a little more testing. Pulling the HDMI out and putting it back in as well as rebooting the fire cube will make the tv see a Dolby digital signal, but shutting the tv off and back on will not. Found that odd.

Yeah it will, although may be able to do away with the switch when you get the arcana, or use it for other items if it fixes the issue. 

Out of interest, have you tried a different HDMI port as well ? 

Yep. Same results.

This should be telling us something, but I‘m not sure what that is. Probably, powering down, then powering up the TV reverts the TV to a default audio format without triggering the EDID negotiation.

Yes. And once it sees the real device capability, it stays the whole time you are on that input. I figured with a physically caused glitch of some type, is see it keep dropping from Dolby digital back to PCM over and over. That doesn't ever occur. I'm going to order the selector you suggested and just hold tight until the arcana arrives. I really appreciate the help.