@cosmic_charlie, I answered your question in your previous Audiogon post and will provide some additional comments.
The Bricasti M1 uses a twin DAC design, the dynamic range for each channel is optimized by using the stereo ADI 1955 D/A converter in a MONO configuration. I heard the M1 at the LA Audio Show and was very impressed. I obtained a demo unit and really liked it in my home system, so I purchased it. I eventually upgraded it to the M1SE version and there was another sound quality improvement.
My next search was to look at R2R DAC’s. I was very interested in MSB Discrete DAC but got very frustrated when I discovered the XLR Balanced Input Module, USB and AES/EBU features I needed were extra cost options. The Discrete comes with one external power supply and the 2nd one is an extra cost option. I reviewed this with MBS and, after some discussion, they recommended their Reference Powerbase for ever better performance. I cannot remember the exact total price, but it was around $18,000+. Unfortunately, I was never able to audition the MSB Discrete DAC, but its total price was more than I wanted to spend.
https://www.msbtechnology.com/dacs/discrete-dac-features/
https://www.bricasti.com/en/consumer/m21.php
In summary, the Bricasti M21 DAC is excellent, and I recommend it. The addition of the M21 substantially improved the sound quality of my audio system. To my ears, everything sounds truly outstanding. The M21 is a world class DAC and is highly recommended. Bricasti supports its products and offered the MDx board upgrade. I installed the Bricasti MDx digital in my M21 DAC and the sound quality substantially improved. The MDx board is an outstanding upgrade and is included with all current models.
Since I never heard the MSB Discrete DAC, I cannot really answer your question. I own 2 Bricasti DAC’s and like them very much.
I suggest you audition both models (M21 w/ MDx and M3) and make your decision. I hope this helps.