@mouldy15
I can help you a little fwiw.
Arcam have been riding on their HiFi rep for a while now, they made warm easy listening stuff, they always have. A few years ago they nearly killed off their entire AV range because it was badly designed and absolutely riddled with bugs, they did manage to claw it back to a reasonable level with the last two gens of amps, especially the current lot, however....
If you want a pleasant sounding but incredibly boring / safe system, then the Arcam is for you - whatever way they implemented Dirac on board was messy and I have yet to hear the Arcams wow me in modest to top end setups.
The Anthems are not as pretty on the outside (arguably) and ARC isn't as tweak-able as Dirac, it simply isn't. But 99.9% of people cannot use Dirac properly, not even the people at Arcam. ARC is a much better set and forget tool with some tweaking - overall it's a much more transparent sounding processor with better bass management and certainly a lot more lively in it's delivery.
The D&M stuff probably has the best HDMI switching and speaker configs but as mentioned their inline scaler even when off rapes the picture and without completely disabling the OSD it will remain on - that aside I think they sound pretty good, good VFM stuff.
ATI & Anthem are have big heritage with power amps, you really can't buy a bad one. Emotiva sound very good too, not as good but better VFM. It's going to give you a high percentage of every other power amps delivery.
Consider your diminishing returns, product reliability, manufacturer support, dealer support and demo where possible - personally, I think it's a pretty easy choice. I would take into consideration also that HDMI 2.1 will address a sh*tload of problems that currently plague users when it comes to HDR and Hz - I don't think you'll see this on any upcoming processors until sept 2018.