@navyachts as long as you are running roon core on a computer and streaming to bricasti over network it will be fine. If Audirvana site is accurate about Bricasti compatibility, it should work exactly the same way - audirvana on your computer, streaming over network, computer away from your system.
Somehow I have a feeling Audirvana sound quality may be better than Roon but I can’t check that in my system as I mentioned earlier my DAC is not equipped with network card.
As to the difference between M21 and your M1S2, I’m pretty sure the delta sigma and DSD sections are identical and the 2 DACs will sound the same. What sets the M21 apart is the R2R section. And many who own M21 prefer its R2R DAC over the delta sigma. Don’t take my word for it though if you’re looking to upgrade confirm this with Joe.