I wouldn't say that the Muse 2+ crushed the smART DI/O, it's different. I found the soundstage to be a bit more open, and the sound to be smoother. The Muse was more suitable for classical and jazz, while the smART had a bit more foward, viseral slam. Great for rock. Take a look at Iron_Dreamer vs. My musical tastes and it's pretty obvious why we picked which DAC.
In the end, the HDCD decoding of the Muse 2+ really gave it a decisive edge. I really do miss it, pretty neat finding out which of your CD's are encoded that you didn't know. When that bottom LED lights up, it's like a newly discovered treasure.
The one thing that I found problematic about the smART DI/O is that it'd output is realy powerful. Maybe it was just Iron_Dreamer's former unit, but it caused a helluva lot of clipping and crackling distortion in my Headroom Little More Power, no matter what the volume was at.
I guess the smART may not be suitable for weaker amps.
-Ed