I have an Anthem MRX520 which does the job very well
I had it looped in so I only used it to drive rears & centre
I now have my music in a separate room so MRX520 deals with all application for AV, very well for the price I would say, too
I think it really depends how important the various sound processing modes are to you. I had an AV2 many years ago, but it quickly became outdated as NAIM decided they weren’t going to focus on home cinema.
I like watching the Netflix/Blu-ray films in Atmos/DTS-X. As a result, I now use an Anthem MRX740 in a 5.1.2 set up. The Anthem is relatively inexpensive (compared to some of my other NAIM kit), and does everything I need. My NAIM amp (282/250) still drives the main two front channels.
I stay with my AV-2 + NAP-V175 because it sounds good in my 3.1 setup, it is compact compared to the Denon and Marantz AV preamps I have used in the past, and it spares me the need to relay HDMI, which I find tiresomely unreliable.
I have a fairly high spec Denon AV Amp with the front L & R Speakers driven through my Naim system using the pre-amp out sockets. I guess you could do this with other naim amps powering all the other speakers? You let the AV amp do the balancing act, and also the balancing software with the mic really helps on setting the levels.
In using the Essence and similar DACs, eight channel LPCM is the preferred format. Devices like the Apple TV (last three generations) can pass this with Apps like PLEX or Infuse decoding Dolby True HD or DTS Master etc. when necessary.
Interestingly, the Dolby Atmos format used by the ATV is also decoded and mapped to the surround channels, though the ‘spatial’ data isn’t used with this configuration.