The new AVR won’t make a difference in how the Cube or Plex HTPC behaves. You could try HTPC now.
TBH, if you want lossless audio (TrueHD + Atmos, DTS-HD, DTS:X) and HDR10 & Dolby Vision, consider a Nvidia Shield Pro (not the tube).
I’ve the Shield 2015 Pro as my main Plex client. It pre-dates Dolby Vision support, but direct plays everything I throw at it.
Shield Pro → Denon 4300 → LG B7 OLED
My “torture test” video is the 4K HDR 60fps version of Gemini Man. It runs above 100 Mbps for almost the entire movie. The Shield never blinks when playing it.
Re: Plex HTPC, see Dolby TrueHD passthrough - modified mpv build . Plex Desktop & Plex HTPC use mpv.io as their underlying playback engine. The thread mentions some work to improve TrueHD playback.
