1) Do the 100's have sufficient power to drive these speakers with ease? (I would think they do but would value another opinion)
D-100B's should drive them just fine... they'll produce 200w into 4 ohms.
D-200 MKII's would be better, but most noticable if you have a large room.
2) Are there a lot of people who use these amps with tube pre-amps? It looks like they would work well with a wide variety of pre-amps.
I'd say it's about 50/50, a lot of our customers use tube pre-amps, but also a lot of passive and solid state.
Due to the high input impedance (100k), our amplifiers work well with most any pre-amp.
3) From a sound quality perspective, would the new 100Bs be preferable to a used pair of the older version of the 200s?
Sound quality of the D-100B is superior to the original D-100/D-200.