I've had the R-900's in my main system for several years now & decided to pull the trigger & ordered a pair of the R11's today! I plan on pairing my old R-900's with another system I have and the R11's will take their place in the main system. Can't wait!
You'll note the bass isn't quite as deep, but it is far better controlled. The highs are about the same, but much smoother and less fatiguing. I've seen reports that lower midrange is a little weaker, so less of the "British bump" we've become accustomed to hearing. Overall, more neutral yet very smooth and musical with better attack & decay characteristics. When I heard the R11's they were powered by nearly $30k worth of new Naim DAC, pre-amp, and power amp. Way too close to Reference series for the price.