Marantz SA 10 compared to

I did not have the Oppo 205, but I had a Benchmark DAC3, which uses a ES9028PRO converter chip, for a few weeks before purchasing the Marantz player. The SA10 is way better than the DAC3 (when using DAC3 with a Sony 5400ES as transport). I could not A/B because I didn’t have them at the same time, but my impression is that it wouldn't be even close. Granted, their price tags are not close either.

I’m sure the Marantz SA 10 is quite a bit better than the stock Oppo 205 for both CD & SACD playbacks. They aren’t in the same league IMO.
The SA 10 is Marantz reference series line and is their flagship CD/SACD player within their reference series line. It’s quite evolutionary upsampling technology used in the SA 10. The Oppo 205 is a spectacular universal / 4k UHD bluray player or AV player and it’s like a Swiss Army knife it does everything quite well and is probably one of the best 4k UHD bluray player in the market. The Oppo 205 audio and video performances over HDMI are spectacular.

However, when you get the Oppo 205 fully modded by Modwright full modifications then sonically it will take the Oppo 205 to a reference quality player for stereo CD/SACD playbacks. The Modwright modifications only affect the stereo analog audio outs (both XLR & RCA). I will be psyched to compare the fully modded Modwright Oppo 205 with the Marantz SA 10. The Modwright Oppo 205 might be the winner. Dunno.

It will outperform the 205 by miles.

I have the Marantz KI Pearl and have owned a Modwright modded Oppo BDP95 and currently have the BDP 105D and UDP 203.   The Pearl is a few notches down the line from the SA 10 and is a much better CD/SACD player than any of the Oppo players I've owned.  The Oppo players are good, but as someone else alluded to, they are built to perform many functions while the Marantz is purpose built for one thing only and does that one thing much better than the jack of all trades Oppo.