Hello all,
I've owned the Dyn1.3SE's, and currently own the Dyn S3.4s and the Dyn Special25's. [Bgarrett]: I would recommend that you not get too caught-up in the specs of the various models you are interested in. The specs are not going to tell you much about the sound; rather only how they measure technically. It's important to remember that each of the models described above has a unique voice and sound.
For what it's worth, I believe that there is a significant performance increase from the 1.3se to either the C3, S25, or S34s. Most notably that the 1.3se tweeter seems prematurely rolled-off when compared to any of the other models. The C3 at medium to higher volumes is a benchmark speaker, however the C3 needs a huge amount of high-quality current; and performs best at fuller volumes in my experience. The C3 is also the least efficient at sensitivity and ohm load. Either the S25 or S34 is an easier load for an amp compared to the C3 and they don't go below 4 ohms.
As always an in-home audition with your equipment is preferred, as long as the speaker is properly already broken-in. Both the S25 and S34 take at a minimum over 100 hours of medium/fuller volume to get them to relax and open-up.
Bigger differences between the S25 and the S34, would be the use of the Esotar2 tweeter in the S25, and the new Esotec tweeter in the S34. Also, the S34 will dig deeper for you than the other models mentioned here, if a fuller range or dvd/film playback is an option for you.
I'd be glad to field additional specific questions if you have them.