I have had 911 in my system for the past 3 months. After comparing it back and forth with my dart, I still preferred the dart. I found the dart to be more musicly engaging, more immediate, with more palpable midrange.
911 had more resolution and bass slam, but was rather uninvolving.
$12k Spectral DMA-260 I had on loan was cooler still, but overall, I preferred it to 911 as it offered more speed and overall transparency.
All listening done with my Puccini / Sasha setup. You may have better resoults with a dedicated Burmester pre (911 has an unussually high gain, and unussually low input impedance) but at least the playing fireld was levelled for all 3 amps.