Ended up buying this Motorla MoCA adapter from Amazon.

Works perfectly with my Fios router. No settings to change. All I did was plug the coax end into the coax outlet. Then plugged the ethernet end into my nVidia Shield. Speedtest was lighting fast (don't recall if it was the full 300mbps). I have had zero issues streaming 4k remux content via Plex.

Just make sure they are MoCA2.0 Bonded adapters. Otherwise, you might be limited to ~150Mbps backhaul.

something like this motorola/zoom or this actiontec

This works well. Full gig speeds. MOTOROLA MOCA Adapter for Ethernet Over Coax, 1,000 Mbps Bonded 2.0 MoCA (Model MM1000) https://www.amazon.com/dp/B077Y3SQXR/ref=cm_sw_r_other_apa_i_OuuADbATVN0V0

I tried buying a moca to ether net adapter to get a wired connection. After buying a $60 adapter(the Motorola one) it didn't I work. After some research I found the signal that the directv adapter sends through the rest of the house is purposely slowed down so you can't do this.

Edit: after re-reading your post, the direct tv ones you mention only go one way, from the router to coax. This might/should work.Motorola adapter