Movie SQ - Apple tv+ vs Smart TV (lg) Aps. Preference?

I have not used the CEC/ARC method to get audio from TV.  It's my opinion that a good source device will always have better audio.

That being said, the AppleTV uses a tiny switching power supply that is built into the AppleTV unit itself.  The power cord is really just a normal A/C power cord with a different plug on the AppleTV side.

If you really want excellent audio/video from a Netflix streaming, I would recommend getting a Roku Ultra streamer and then buy a nice linear power supply to replace that switching "wall-wart" power adapter.  The current Roku Ultra uses a special size 4.75mm x 1.7mm DC plug, so you would have to ask the linear power supply company for a custom cable (such as Teddy Pardo or Farad or Teradak).  Even a cheap china Teradak power supply would give you excellent results.

Sad apple tv 4k box does a crappy job with power which likely hurts sq abit. Video quality is fine, i think.

Video quality is generally pretty good with these streamers when using the stock switching power adapters (i.e. Amazon Fire TV, Roku, AppleTV).  However, you would be amazed on how much better the video quality is with a linear power supply.  I tested this side-by-side watching the same move streamed from Amazon services.  I used the current model Amazon FireTV Cube, which was good.  However, when compared to a Tivo unit with a Teradak linear power supply doing the Amazon streaming app, the Tivo just blew away the FireTV in video quality (as well as audio quality).  The video picture was just so much cleaner and more solid and colors were more saturated.  There was an element of video noise with the FireTV and wall-wart power adapter.  Obviously, audio quality (over HDMI) was significantly better.  Audio did not have the harshness/brightness of the FireTV and sounded much more natural.

this in an interesting discussion.  In theory then Blu Ray from a dedicated player with a superior power supply to ATV should also sound and look better?  I've always noted the superiority of dedicated players versus the ATV in my HT systems but always attributed it to problems with the stream itself and not factors such s power supply.

Does connecting to a power conditioner help or is linear power a better way for a streaming box?

There is limited commentary out there, except herein, about sq issues when using a streaming box like apple tv or roku, etc.

Generally speaking, bluray discs will have better audio and video than streaming because streaming is usually somewhat compressed video and is limited to Dolby Digital audio.  Bluray has better video resolution on the disc and also provides hi-res bluray audio formats (DTS-HD MA and Dolby TrueHD).

That being said, I think you may be able to get better audio/video from a Roku streamer if you use a linear power supply on the Roku.  This is because pretty much 99.9% of bluray players out there will actually have a switching power supply.  Some may have linear power supply for analog audio output (i.e. oppo 105/205), however they still use switching power supply for digital/HDMI.

Here's an old thread that I wrote up:

https://forum.audiogon.com/discussions/musings-on-switching-power-supplies-lps-for-oppo-directv-radi...

If you get a Oppo or Panasonic bluray player and then upgrade it to linear power supply (i.e. Oppomod website or others), then it is likely to meet or beat a Roku with linear power.

A power conditioner may help a little bit on the streaming box, but you are still using a tiny switching power supply.  A "Linear power supply + Roku" would be highly superior to "Power Conditioner + Roku".

In all my testing, R&D, modifications and experience, the power supply is the single most important factor in most audio electronics.

Bluray player is tough due to viewing limits.

so linear power is path to get better sq.

seems easy.  

A Roku Ultra is the best choice if you want a streamer that you can upgrade with linear power supply.  It uses a decent size DC plug (it's a 4.75mm x 1.7mm).

The AppleTV cannot be upgraded because the power supply is internal to the box.

Amazon FireTV Cube uses an even smaller DC plug (4mm x1.3mm) and it's a pain it the butt to wire.  This is not recommended.

The Tivo Edge DVR can also be used to stream (Netflix, Hulu, Amazon, HBO, etc.).  I think it uses the larger standard size 5.5mm x 2.1mm DC plug, but you would have to make sure.