What receiver features are must have these days?

Hi all,

The last time I was putting together a home theater rig was around 2010, so I'm not up to speed with the current tech. Can someone explain what are the features to have in a receiver? I usually buy used. That will likely be 7.1.2 setup (FL, FR, C, SL, SR, SBR, SBL, Sub, and two height speakers). All Monitor Audio radius series speakers. The issues I've been having with my current Denon AVR-2310 is unreliable surround passthrough support (most often I only see two channels on the receiver, coming from Nvidia shield 5.1 or full Atmos source) - I noticed this problem more with new .mkv rips. Looks like my old receiver does not understand them. Also correct lipsync is a problem. Do I need e.g. eArc?

Any help would be appreciated

​

​