What should I upgrade next in my system?

I agree with @mclinnguy that it’s difficult to answer your question for the reasons stated, but IMO, the most seamless way to start is to upgrade your digital source. I’ve owned the Oppo 205 and I think that any $1000+ dac will be quite an upgrade. You can use the Oppo as a transport for starters. You can still play SACDs directly from the Oppo, but I think that Redbook through the dac will sound better than SACDs through the Oppo. As to what dac to buy, there are tons of threads here on that. Check out the dac shootout thread by Verdant. Whether you want to get into streaming is another issue. I personally do not stream, so I’m not going to opine in the merits of streaming. But I do think your source is currently your best path for an upgrade. The Oppo is a great jack of all trades, but, IMO, the sound cannot compare to a good dac. Be well .

Room Treatment (treat your room)

Thank you for all the great ideas. Even though I subscribe to both Tidal and Qobuz, I mostly stream through a 4K Apple TV using YouTube Music. The reason I use YouTube Music is because I like live video with my concert recordings and they seem to have the most live concert videos, and the sound quality through the Apple TV seems to be pretty good. I have a 120-inch Sony laser projector in a dedicated media room. 90% of my time in my media room I am watching concert videos such as the Eagles in Melbourne, John Mayer in LA, Tears for Fears live from Village Studios, Steely Dan, Morgan Wallen live recordings from Apple Studio, etc. I use the Oppo 203 as the source when watching Blu-ray versions of these concerts, concerts I download to my 5T Seagate hard drive from the internet, or very seldom a SACD. Even though I have a nice set of surround speakers, I listen to two channel 95% of the time though the Martin Logan 15A's. I have some acoustic treatments in the room, but because of the room size, I am somewhat limited. All my previous rooms where filled with ARC treatments. It definitely sounds like upgrading the Apple TV is the way to go, but how do I do that without losing the video component or making the system overly complicated? Kaleidoscope seems excessively expensive, and I do not watch many movies, mostly only concerts, which I find easily through downloads onto to my multiple 5T Seagate hard drives which are totally full of concert videos I have found over the past 30 years.

I also agree with post by @mclinnguy … it is difficult to answer until his additional questions are answered.  Your speakers and amplification are solid performers.  However, I cannot comment on the theater processors you are using for I do not have any experience with these units.  I also recommend starting with the digital front end.  If your budget is $30k, I would spend half on a DAC and half on a streamer/server.  My favorites that get you to near world class performance are a Mola Mola Tambaqui or Bricasti M1 with an Aurender N20, preowned W20SE or Grimm.  

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.