HDMI can convey audio formats not possible via S/PDIF coax or optical. You'd be able to access HD formats such as Dolby TRyeHD and DTS-HD Master Audio as well as multichannel PCM. Opticall cannot convey these HD formats which are commonly used in association with films sourced via Blu-ray and UHD discs. You'd also need the ability to bitstream TRueHD or Dolby Digital Plus (DD+) if also wishing to access Atmos. THese 2 formats are what the associated metadata is ordinarilly packaged with. Neither TRueHD or DD+ can be streamed via optical.
If the differenf TVs and devices you are outputting to have different video capabilities then the AV receiver will inform the source device of this and the source would limit its output to what all the devices in question can handle. This would limit you to the lowest resolution and no, out of the outputs are not independant and will not be scaled independantly.
From the manual:
- If both the HDMI MONITOR 1 and HDMI MONITOR 2 connectors are connected and “Resolution” is set to “Auto”, the signals are output with a resolution that is compatible with both TVs.
When the “Resolution” setting in the menu is not set to “Auto”, set the resolution in “Video” - “HDMI Monitor 1” and “HDMI Monitor 2” to one that is compatible with both TVs.
- You can check which resolutions are compatible with your TV in “HDMI Monitor 1” and “HDMI Monitor 2”.
- When connecting multiple Dolby Vision TVs, the signal will only be optimal for one TV. A TV connected to the HDMI MONITOR 1 connector has priority.
Note that if using the dedicated secnd HDMI zone output that both the video and audio would be passed through the receiver to a second zone without the AV recever playing any part in processing it, but if the source is simultaneously also be used by the main room them you'd still be restricted by the capabilities of the least capable display.