Don't use ARC - use a Toslink cable to your MC-700.
What about using a 4K Fire stick or Roku box instead? My understanding is that they are likely to have faster processors. Also, I've had few or no A/V syncing problems with my HD versions of these devices.
7.1 Home Theater: Oppo BDP-93, Roku 2XS, Gen 2 Fire stick, Comcast X1 STB, MC-700, XPA-3, UPA-500, LG OLED65B8, Polk VM30 (2), VM20 (4), Emotiva C2 (center) SVS PC12plus
Old School Stereo: Linn Basik w/ LV-X tonearm & Sonus Blue-Gold cartridge, ERC-2 , XSP-1 , XPA-2, Dahlquist DQ-10 (2)(w/ Regnar x/over mods)
5.1 System: LG Blu-Ray, Gen 2 Fire stick, Comcast X1 STB, UMC-200, XPA-5 Gen 2, 50" Panasonic Plasma, Polk VM30(2), VM20(1), VM10(2), SVS PC12-NSD
Of course, but since you have been using and subscribing to both Roku and Amazon, you should be perfectly capable of deciding for yourself.
You don't seem to have read what I wrote.
I believe he means the 4k versions will work similarly so the things you like or dislike will still be present, just in 4k. So if you like either, get them.
The risk is the MC700 has only HDMI 2.0a ports. I don't know how well (or not) that will work with either of those devices and their 4k versions, and your TV. The MC (which I have) has it's share of Emotiva HDMI warts, especially with 4k.
So, I've just spent the big bucks and ordered a 4K OLED TV, and now it appears my cable provider may not be able to provide me with 4K source material. Fortunately, we have pretty fast internet.
Should I get a 4K Fire or Roku source, or just rely upon the apps in the TV (LG)?
My concern is that using the TV apps means I will have to rely upon ARC to get the audio signal to my MC-700. Is that likely to restrict my sound quality or options?
I have the Apple TV 4K and I am very happy with it. ARC should send a DD 5.1 signal to the MC-700, which is really not bad at all. I personally prefer the Apple TV interface to the built in apps on on television, but try the apps out on your LG first. You may end up being happy with it. If not then look at the Applte TV etc.