Denon AVR-S510BT - HDMI 2.0a/ARC questions

So i'm getting a Sony XBR75X940D soon, and need a new 4K/HDR receiver for my 5.1 wall-mounted speakers. I'm deciding between the Denon AVR-S510BT, or the next model up AVR-S720W.

Now I love Gaming a lot, and I'm getting the Xbox Scorpio next year, and so I of course want a TV/Receiver that can handle both 4K/HDR. I'm good with the TV, but i'm a bit confused on some aspects of the Receiver.

Firstly, here's my current setup(new 4K setup will be the same, just with TV and Receiver swapped for new ones): Xbox Game Console/PS4/Cable Box---hdmi--->Receiver---hdmi--->TV. Receiver is connected to pre-installed 5.1 wall-mounted speaker system.

So with the above info, here are my questions:

1.) Firstly, regarding the S510BT, i've read the S510BT at launch didn't support HDMI 2.0a/HDR. But an upgrade would/has made it 2.0a/hdr enabled. Do the current ones being sold now in Nov 2016 have the DTS:X firmware upgrade enabling HDMI 2.0a/HDR already pre-installed? Or do I still have to update it manually myself? And which HDMI ports on the back of the S510BT become 2.0a/hdr enabled?

2.) Secondly, I've read the S510BT doesn't have Audio Return Channel(ARC). The S720W does. Do I personally need ARC on my setup? I mean, will I need a second optical cable to get sound through my wall-mounted speakers with the S510BT since it doesnt have ARC? Or will 1 HDMI cable from each console/cable box to the receiver get picture and sound through that 1 cable since the audio/video source isn't the TV itself?(The source will be the cable box and the game consoles.) So does it matter for my setup? Do I need it?

Every other difference between the 2 doesn't seem to matter to me. I dont need things like 'HDMI to HDMI Scaling' or certain 'Sound Enhancements', right? Unless there's something else i'll need you guys could tell me about, I think that's all. Would appreciate some advice/clarity. Thanks in advance.

EDIT: Also noticed the AVR-S710W. What's the difference between that and the S720W? Just less ports? Are they exactly the same otherwise?

Submitted by Adam802 | #Specialdealer Special Offer Online Shopping Store 2016