I believe all the CODECs will work in 7.1 configuration and be available in 44/24 or 48/24, I will miss overhead channel info. Im very interested in using a HD621 to try different DACS, adding a Meridian and replacing the AV2 is an option especially used as I can only run 8 separate channels with Meridian any way. I only run audio from a UHD player to the audio set up, the HDMI picture goes direct to the PJ, via a Lumagen. So pass through is not relevant to me.
My current set up is Panasonic 9000 (with added LPS and slightly modded analogue board) > naim AV2 to 9x 135’s (with 32.5/spercap in loop for L,R these are bi amped) to Sonus Faber Extrema, Cremona C, Elipsa, Amator, Rear and surrounds.
I did have the Acurus in replacing the AV2/32.5-supercap for about 6m, but on the final reckoning the Acurus was better with resolution, positioning and backdrop. But it missed the groove of the naim and I decided that it was better to sell and pursue analogue out than experiment further with other £12k processors. I could see some preferring he Acurus in place but for me the resolution is not something I pursue, I’d rather be moved by the music and emotion of the film than hear every detail. (The Acurus isn’t overly detailed or analytical, but try as I have over the last 10+ years I move the 23.5/superCap away from driving the Extremas and I lose something)
I will need to move house (on the market at the moment) before I invest in 4 naim DACs as I will need more rack space and for space but the idea of say £5-6k on a HD621 and 4 naim DACs just seems to have more potential for happiness than say a Trinnov (I have heard it several times, and whilst it is extraordinary for spacial positioning it left me cold with emotion and music. I greatly respected it but didn’t covert it)