The Dynaudios's woofer is in a complete different performance class in terms of bass extension and integration with the tweeter--it's a 1st order crossover and basically acts like a point source. Tweeter wise, it's much more laid back, and tends make everything sound smooth.
S2s are also quite tonally different from the C1s. Compared to the C1s they sound brighter and much leaner, with more details in the highs. The C1s are have a ton of more bass extension and slam and are much warmer.
If you are considering used, I have seen Paradigm Performa Bs go used for around $4000. I've heard demos in show rooms and they have the slam and bass extension of the C1s but also have much more treble extension, the best of both worlds. I think they might be the best 2-way monitor you can buy right now.