Add an external DAC. Make my Oppo UDP-205 a true top player

dcaudio
It would be difficult to improve upon the 205.  I have one and it is approx equal to my W4S Dac (latest model- but sold).  It is however behind the Matrix Audio X-Sabre Pro that I now have. All three of these run the latest ESS chip.  As a suggestion you can get a small - very small - improvement in your Oppo if you (1) open it up and place some dynamat inside, especially over the drive unit; and (2) place the unit on Sorbothane footers.  (3) Ensure it is level. (4) Depending on your preamp and other gear there may be some benefit in using the balanced XLR connection. 
I had an Accustic Arts Dac in my system for a two week trial.  It had tubes and produced a very polished sound.  It also looked good on the shelf.  In the end I did not go for it as the improvement over the W4S was not sufficient to justify the large price. 
For a sideways move you can try a Marantz or, better still, a Dac by Gieseler Audio.  They are based on the AKM chip.  
Apart from that you have to move to FPGA or Ladder resister type.  I have not heard either of these types but they are expensive.  
Andrei

i bought a NAD D1050 DAC that i use in conjunction with my Oppo 103. much better than the DAC in the 103. the pair sound phenomenal, but i would be interested in what others in the Oppo community have experienced. i originally considered the 105 but the 103/NAD combo sounded better and cost was about the same.  i heard the 205 and think it's much better than the 105, maybe less edgy, very textured, full sounding.  the 205 would be hard to beat, but just try and find one now.  the prices have gone through the roof.  RIP Oppo

I have a small room for video so I made that system compact and 2 channel. In addition to a 65 inch OLED panel hanging on the wall, I use a UDP 205 going straight into JBL 705P monitors on stands via XLR. Results are very impressive. I also have an NAD M-10 in the big system in my living room and a Bluesound Vault 2i in the TV room. Everything is tied together by CAT 8 ethernet cabling. 
Naturally I wonder, at times, about what might be achieved by upgrading the DAC in the TV room beyond what OPPO has provided but, since I'm very impressed by sound I'm getting and I feel no need this late in life to chase SOTA, I never get past musing.
Try those little JBLs if you have a 205. I think you'll be shocked to find out what you are sitting on from OPPO.

Bel Canto 2.1:  $2,795 on amazon 

Take a look at the Lampizator Amber 3 DAC or read some posts on Audiogon and reviews in general.  I am using this DAC with my Oppo 205 for redbook CDs and for Tidal/Roon streaming via the Nucleus+.  To my ears it is the best DAC within a reasonable price point.