What should I upgrade next in my system?

+1 @deep_333 Think of the room as one of your most important components.

How bad is the 4K Apple TV streamer and Anthem processor I am currently using for Tidal, Qobuz, and YouTube Music? I assume pretty bad...

Better than Apple TV can be had for sure. Easy peasy.

Given your home theater set up @rickguild using a vendor to jigger your system might be the way to go. Most of us here are two channel sit in the chair and listen types. Period. There are some RtoR types but most members use vinyl and/or streaming. I’m all in on Grimm streamers (their one box combo or their unit with a stand alone DAC) too but at that level there are plenty of others just as excellent. But the room makes such a big difference. So there’s that.

@rickguild No, your Anthem prepro is the heart of your multichannel system and shouldn’t be going anywhere.

These are 2 channel guys on this forum, who are probably quite confused about your rig.

A higher quality streamer transport into your Anthem prepro could possibly improve the sound quality. But, no, you wouldn’t need a 10000 dollar streamer for that??!! Try maybe a 300 dollar Wiim Ultra streamer as the transport into your prepro, with lots of other user friendly features. I know your Anthem prepro won’t let you do any manual PEQ, etc.

A power conditioner such as the Audioquest Niagara or PowerQuest 707 will improve the sound.

The most important thing on multichannel rigs is room treatment, but, if you are set up in a living room and wife won’t let you, well.... there’s your bottle neck.

On a different note, your Anthem Prepro is now almost 10 years since release. A sonic upgrade for it might be the newer Marantz AV10 prepro. But, you need to know how to set up a prepro, read the manual from cover to cover, run a calibration correctly, do finer tweaks from there, etc, ask questions on avsforum maybe. The Marantz AV10 already came with all kinds of streaming feaures and a great DAC where you didn’t need any other dacs or streamers...no Grimm...no Brimm for 10k needed..

I appreciate the DAC and Streamer recommendations, but my budget is probably not 30K (even though it was on my speakers) until I am convinced that spending 10K on a previously-owned DAC and Streamer does not get me 90% of the 30K performance. Am I wrong in thinking that?

Would the new DAC and Streamer eliminate my Anthem AVM 60 Preamplifier and Processor from my system? If so, how do I use my Oppo 203, Cox Cable and Apple TV through them?

How bad is the 4K Apple TV streamer and Anthem processor I am currently using for Tidal, Qobuz, and YouTube Music? I assume pretty bad...

I do love how easy the 4K Apple TV is to use.

Am no Apple TV expert, but if you’re streaming videos, you can use an external dac for the audio portion but you’ve got to use the apple tv streamer for the video portion (I think).  You can get a better streamer for Quobuz and Tidal, but of course you won’t be using that for concert videos.  So, if your use case is watching videos, a new dac is your priority, not a streamer.

one other thought: if your primary source is youtube, that’s compressed, lossy audio, so you shouldn’t spend a ton on a DAC, IMHO.  But you’ll probably be able to hear substantial improvement spending less than $1000.

@rickguild I think this is right up your alley: 

https://www.linn.co.uk/ca/network-music-players/selekt-dsm

https://www.whathifi.com/reviews/linn-selekt-dsm-edition-hub

Find a Linn dealer and see what this box can do for you. It is totally configurable based on how much you want to spend on the streamer/DAC/processor portion, it contains all the modern video DTS and Dolby processing and with HDMI switching module you just connect various inputs like gaming or your Apple TV into it, and can even contain built-in amplifier modules (you probably don't need). It has Linn's own proprietary room correction which looks interesting, and this is set up by the dealer not by the customer- nice approach. 

If you want to get an end game streamer and spend crazy money look at Klimax DSM:

https://hifiplus.com/articles/linn-klimax-dsm-network-streaming-preamplifier/