I wouldn't say that the 650a will properly drive R100's however as long as you're not after constant disco like levels then i owuld say the 650a has got sufficient quality and quantity of power to cope with R100's.
Btw, what areas of improvement are you looking from a new pair of speakers?
I would like to have more detail and bigger, clearer sound. The DM685s are great but a litte muddy sometimes. I also have the b&w 608 sub, but I think that I will have to replace that to a velodyne as well if I will go for the upgrade.
I think that you should also look at ATC's SCM7 monitors. SCM7's benign load, closed box design, low distortion, flat and honest presentation help reproduce soundtracks with (amongst their other qualities) in an uncoloured, controlled, clear, detailed and natural manner. These qualities also make it far easier for SCM7's to integrate with sub woofers.