I can't personally comment on the axon/solen 100uf caps. I did my initial upgrade from the stock caps in the Spring of '11, after parts connexion had already sold out of their 100uf stock. So I bought the 91uf version instead. To my ears, the obbligatos are definitely worth the ~$50 premium over my old axons. The sonic differences between these caps is about on the same order of magnitude as rolling various well made 12bh7's.
If you check out the cap comparison at www.humblehomemadehifi.com/cap.html , the author describes the axons as good budget caps, having a slight "focus in the lower treble range" and lacking in air and micro detailing. I haven't compared very many different caps, and wouldn't try to describe the differences to this level of detail by ear even if I had. But with the obbligatos, I am finding the trebles to be just a tad less prominent and more natural sounding (closer to live instruments) and that deep bass is improved in quality and quantity. (Again, I assume the change in bass stems mostly from the 9uF increase in capacitance, as several of the threads on bh discuss how deep bass rolls off as you decrease the capacitance of your output caps.) These were welcome changes from my perspective, particularly given that I spend the bulk of my listening time with hd800's (that do not require any added "focus" in the lower trebles).
For example, in addition to my ordinary array of well recorded test tracks (e.g. k2hd jazz at the pawnshop and we get requests, simon&garfunkel - live in nyc, mfsl gold ella and louis again, chanticleer - evening prayer, songs for distingue lovers, etc.), I decided to throw on some 2pac (all eyez on me), to see if I was really hearing things right down low. Lemme just say, the bass was hitting hard, in a good way - a way I did not expect to hear from flagship open Senns. Needless to say, I'm really enjoying my crack these days!