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Re: What ROKU device works for a 4K PC Monitor w/o TV?
AVR is audio-visual receiver. It's just a receiver with HDMI input/outputs. That way your monitor doesn't need speakers.
As to what Roku you should consider, I'd say any of the 4K capable players. The Ultra is the only one that offers an Ethernet jack, and also offers Dolby Vision. However, it's unlikely you'll find a computer monitor that supports DV.
But unless you have very special requirements, you can likely find a nice 4K TV for less money than a monitor. I just bought a 40" Vizio 4K TV that I use as a computer monitor while I'm teleworking, and also have a Premiere connected to it, and paid about $200 for it.
Dan Ultra (4640), Ultra (4670), Ultra (4800), Premiere (3920), Insignia 720p Roku TV, Sharp 4K Roku TV, Nvidia Shield, Windows 10 Pro x64 running Serviio and Plex on a wired Gigabit network.