Just bought a Sony A80J and I having issues with it and my Yamaha RX-V679

Sorry if this is a simple and commonly discussed issue. I simply don't even know what to search for to see the answer. lol

I just bought a 77" Sony A80J and want to use my Yamaha RX-V679 but I'm having some issues and have a few questions. The main issue is that I cannot get sound to the receiver through any HDMI connections. I can only get sound through the optical connection.
1. I am using the built in Sony platform for all my streaming services. It's as good or better than my Roku Ultimate so I wanted to simplify things.
2. All firmware on both devices is up to date.
3. I am running a 5.1 speaker set up with a decent set of Polk speakers...nothing special but good enough for me.
4. When trying the HDMI sound option I am using the eARC ports on both devices and have tried other ports.
5. All cables are rated appropriately and I've tried different cables...again all rated properly for these ports.
6. I don't use this room or setup for anything other than movies/tv, so streaming music or any type of other music device is irrelevant (turntable, etc....)

So here are my questions.
1. Am I losing anything by using the optical instead of the HDMI?
2. If I am not using the upscaling of my receiver, doesn't it make more sense to use any devices (Nintendo Switch, Apple TV for my yoga programs, etc...) through the TV instead of the receiver?
3. Would I be wasting money by buying a new receiver if I am only using it for audio because the TV would probably be its equal unless I spend a decent amount of money on the receiver? I don't have a problem dropping 1-2k on a new receiver if it will genuinely offer me a large upgrade in sound.

This is my first foray into a setup of this quality so excuse my ignorance and thanks in advance for any help offered.

Oh, and the picture on this TV is unlike anything I've ever seen, it's stunning.