For my setup, I don't use or need ARC/CEC. So I use an optical cable from the C8 to the 780 for Comcast audio. I have my Comcast STB connected directly to the C8 for local HDTV stations only. I do this because I have legacy cable boxes (1080 only) and they don't play nice with Deep Color so I need to connect the cable box directly to the C8 and disable Deep Color on that input only. Local HDTV is 5.1 audio only so that's why I use an optical connection. All of my streaming is via an ATV4k so I don't bother with the on-board apps. ARC, like optical is limited to 5.1. Some ARC systems can pass DD+ so you will get lossy Atmos. eARC allows for HD Audio (Dolby TrueHD, DTS-MA, lossless Atmos, etc) but is not possible with an optical connection so you need to enable eARC on your devices that support eARC. ARC compatibility does not automatically mean you have eARC ability. That depends on what the device mfr chose to do. CEC, like I said is a pain in the ass so I've disabled that function on all of my devices and just use a programmable remote like a Harmony to control all of my devices with a single remote. For example, you can press a button on the remote that says Watch TV and the receiver, cable box, and tv turn on. You can then control volume, change channels, etc. Or, you can just select Devices, and then select which device you want to use and have almost complete functionality for that device like you would have with its own remote.
All of this depends on how much control you have over ARC/CEC on your connected devices. Some devices allow for separate control over ARC/CEC, a lot don't, so it's either/or. That's why I use the 780 as my hub for the ATV4k and the UHD BD player, and just use optical for the local HDTV stations. Whether your dish remote can be programmed as a universal remote I can't answer. CEC (Consumer Electronic Control), in theory, will allow for that but compatibility with other devices can be a problem. All you can do is try. Being as your system is a little more complicated than mine. I don't have a need to connect my laptop example, and if I do, I just use Airplay. I would write down your connection setups and then see what works. If it doesn't try another configuration setup and keep track of what works and what doesn't. You may have to compromise on something.
Thank you for the detailed response. So here's the current situation:
1. My AVR (Yamaha AX-R780) is connected via HDMI to my Dish DVR.
2. The AVR HDMI out is connected to tv (LG oled c9). External sound and video for all the channels, dvr and included apps (Netflix, YouTube, etc.) work perfectly.
3. I hooked up my blu-ray player (Samsung BD-P3600) the exact same way.
My AVR (Yamaha AX-R780) is connected via HDMI to my blu-ray player. The same single AVR HDMI out is connected to tv (LG oled c9).
The blu-ray and dvd discs display an excellent picture but there is no sound.
There is no sound whether earc is on (with CEC on) or off.
I tried changing audio out on blu-ray player from PCM to bitstream. No change.
Also, none of the apps included with the tv have any sound either.
Am I going to need an optical cable for the blu-ray player?