spaz, I use the RA opus 21 with the GNSC ref upgrades with the Ridge Street Audio Exousias umbilical. I have compared this setup to far more costly digital setups and love what it does for digital. It is a very "analog" sounding player. The opus in stock form is amazing. I have not heard the SF player, however digital has greatly evolved since the birth of the cd1. The opus uses the pcm 1704 chip set which I think ranks up there amongst the best. I am sorry I can't offer comments on a direct comparison between these two players, but only convey how great the Opus 21 is in stock and modified forms. I hope this helps.
Darrin
Darrin