Let me throw my hat into the arena. I currently have the D-30R andauditioned the D-20R and D-48R. The D-20R is a different animal thanthe D-30R/RS. Its leans slightly to the darker, richer side of the musicalspectrum. It excels with vocals and the imaging is some of the best I've heard in a demo. The D-30R/RS is more of a mini D-48R. More extensionand control in the bass, more transparent mid-range and better dynamics. Given how similar they look its surprising how different they sound.
My experiences with the ribbon tweeter have all been for the positive. Heck, I'll go on and say it was one of the features that sold me on it. I've found them to be smooth,extended and refined. Of all the speakers I auditioned the Proac's top end was the best I've heard.
Good luck on your quest.