My system is setup like yours. I run ARC from the TV into my HifiRose streaming DAC or Classe preamp and it works well but there are many times where it doesn’t get the “handshake “ and I need to switch sources and then it works. Optical is more reliable than ARC, but in some rare instances ARC is capable of better resolution. I would be willing to bet though that the resolution between the two is identical most of the time. You may run into audio sync issues and again, that’s a power on/off and/or switch sources remedy to fix it.
TV audio into DAC via eARC or better
My HiFi system is also in my main living room which has my largest TV for movies. Currently running optical audio out of my Sony TV into my Schiit Yggy. It's ok but something is missing for sure. Xfinity 4K box is HDMI only. Apple TV is HDMI only. I would think the highest possibly resolution would involve eARC.
I noticed the Lumin P1 has an eARC HDMI port. Looks like it can also switch video sources but my preference is to keep video quality going straight to the TV.
I know my compressed version of Batman on Netflix from my Xfinity box isn't going to be great but I need something better!
Thoughts? Thank you!