I have both the Apple cube and the Roku here at home. I have been testing the Apple not just for quality but for ease of use as it will be going to a grandparents house as a gift. I haven't used the Roku in over 6 months now so i'm scraping my brain a bit on specifics.

Apple likes:
Upon first use, i felt like its visuals were sharper than the Roku. However, i did not compare images from the same source/channel necessarily (e.g. load up a film from each, some Avenger 4k movie and flip back and forth). I might be able to set this up, maybe. It is also possible that image is just a bit different in regards to how the visuals are rendered between the Apple and Roku regarding brightness, tint, etc.

The remote battery is incredible for energy efficiency. After six months, the thing is still over 50% charge and been used several times a week. Remote can control the AVR volume.

Sound is good but cannot confirm Atmos (i have a 7.1 setup).

I can get Bell Fibe.

Apple dislikes:
Sound input to the Denon AVR was a bit confusing to figure out especially as to which unit was actually processing what. Not sure there are options to process sound via anything but the Apple DAC.

The remote is small and ours has the swipe rather than the 4 point thumb touch. The swiping is not accurate and can be annoying.

The unit occasionally disconnects from our router, loses the wifi (or acts like that is what is happening). Seemed to corroborate this a bit by turning on the microwave upstairs. All that being said, wifi should be re-established and sometimes it doens't and it just hangs such that it doesn't matter what app you try, it cannot connect. The only way to reset is to go to the settings and restart/reboot the unit. This could be something specific to our Asus routers as it does seem that other Apple devices in the house occasinally have dropouts even though the signal strengths are strong. The Roku never had this issue and neither does my Google phone or tablet. Damn Apple crap.

You cannot rearrange the apps on the main page.

Expensive.

Roku likes:

Main page customization.

Easy menus, more slick than Apple.

The remote is also small but way less thin than the Apple and easier to grip, uses a 4 point thumb system. Remote can control the AVR volume.

Sound comes up clearly on the Denon as Dolby D....instead of an obscure entry (i have another post on this somewhere).

Very cost effective compared to Apple (got mine for less than $70 on sale while the Apple cube was over $200!

Has a good phone app as a backup if the remote craps out.


Roku dislikes:
No Bell Fibe app.

The unit attached to the AVR MUST be plugged into a wall socket or the battery in the remote drains in days (something to do with the two trying to communicate constantly yet when plugged in they stop; obviously a glitch, not sure if they will/have fixed it but have seen complaints on Reddit about it)

You have to work your way around NOT giving Roku your credit card info just to get an account to login. Apple may have your cc info with that account anyway but at least you can exclude this if you search for how to do it.

Note that video quality for both units definitely put out 4k images. Quality varies depending on the channel and source material. I'll try to do some comparisons of visual quality with a fixed source such as National Geographic channel.