ethernet connection for Netflix amazon etc.

I suppose you could try using ARC.  However, ARC and eARC uses one single-ended data wire in the HDMI cable (usually not even a good wire).  Whereas HDMI audio from a streamer source uses the combination of the four fully balanced HDMI signal wires (these are the important wires and are usually much better engineered in an HDMI cable).  The power supply and digital circuits in the TV are usually not as good as something that is in a Zappiti or Zidoo streamer. 

The ARC and eARC stuff was developed more for people who just want to mount a TV on the wall and expect it to "do everything".  Also for people who want to simplify and consolidate their systems without any concern for sound quality.

Neither is the right solution.  First, HT processors don't have video streaming apps built in for stuff like Netflix, Amazon, etc.  Some will have internet audio streaming apps for Pandora, Spotify (the MX122 does).  Second, doing the streaming using TV is good for video, but audio quality will take a dump. 

You are best off looking to get a dedicated streaming device.  The streaming device is just another source like a Bluray player or a satellite receiver.

For the cheapest ones, look at Roku or Amazon Fire TV cube.   If you are planning on streaming Amazon, do not get an AppleTV.  Amazon has limited it's Apple iOS player to only 720p and stereo audio (their way of influencing customers to buy their FireTV instead of AppleTV).

If you want a better quality streaming (especially for audio), you can look at the higher end media streamers such as Zappiti or Zidoo.  The more expensive models even have linear power supplies (which further improves both the video and audio quality of stuff over HDMI).

The video quality will likely not be better (but maybe).  With a streamer you are dependent on how good your HDMI cables are.  It also depends on how good the streaming app and receiver is in the OLED TV.7   I think the audio quality will be better though. 

Actually, I plan to get the Zidoo UHD2000 sometime this year.  I'm looking to switch to streaming instead of DirecTV satellite.

If you want to reduce your costs, you can buy a Zappiti One SE ($349) and then get one of those Teradak linear power supplies from ebay for about $200 or so.  It's the linear power supply that makes the major difference.

Amazon limits the resolution to 720p and audio to 2-channel stereo on all iOS devices such as iPhone, iPad, etc.  However, the Amazon resolution is not limited when using an Android device (android phone/tablet and any media player that uses Android O/S such as the Zappiti or Zidoo players).  If you know for a fact that the resolution is not limited on AppleTV, then maybe it is the exception.  NOTE: that the AppleTV could still be outputting 1080p or 4K to the TV, even though the Amazon app is limiting the resolution internally.

As regards to Erik's statement.  I have evaluated the Amazon FireTV cube.  It is surprisingly good for a small device that uses a switching wal-wart power supply.  However, the sound is a bit bright and harsh.  I compared this to a TIVO unit that is using a Teradak linear power supply and tested Amazon streaming.  The TIVO unit with linear power supply just blew away the FireTV cube in both video and audio quality.  Video was sharper and more saturated and bolder in color.  Audio was extremely good without any harshness.  Both of these were tested using the same HDMI cable into the same TV.

Also, not all HDMI cables are created equally.  They all have different results in both video and audio.