I own a Bryston BDA-1 and currently use an unmodded Sonos player. My Rotel 1560 receiver is the weakest link. Speakers are B&W 804 diamonds. I also recently had the very good fortune of demoing Bryston BDP-1 alongside my Sonos, connected to the BDA-1 via AES/EBU.
The Bryston BDA-1 made an incredible difference in the quality of the music through the Sonos. There was just clearly no comparison, and I could never recommend the BDA-1 enough.
The Bryston BDP-1 made a startling difference over the Sonos. Music had an unsuspected 3-dimentional feel to it. The same music (my bit-accurate CD rips via dbpoweramp) sounded... live? There was a distinct location to each instrument... not a "general" location. I did try a few recordings and was underwhelmed though. I don't think this is ANY fault of the BDP-1. Rather, I think it's the source material. It did NOT make them sound bad. Rather, it just didn't improve them as much. With respect to sound quality, I can't recommend the BDP-1 enough for active/critical listening.
Again, that was all comparing Redbook CD music, not HD. I can only assume the HD music is at LEAST as good, if not more so.