Not familiar with how Sennheiser's sound but I imagine its similar to my experience with the AKG K-7XX. Everybody raves about that headphone so I tried it....sounded not like what I was expecting it to, flat out boring sounding and muffled. When I picked up the SHP9500's the AKG K-7XX then no longer were of any use to me, the SHP9500's were better in almost every way to me for nearly 1/4 the price - couldn't take the K-7XX anymore. The only thing the K-7XX has going for it is how they fit on the head...that is quite a nice, light comfortable fit that also is very secure on the head...amazing how they are able to do that. Really, I have not been impressed with many high end phones I've listened to with the special amps that are supposedcto bring out their best, the only one I really am impressed with so far has been the low end STAX (which I much prefer over the high end STAX).
The Fostex TH-X00 Purpleheart is my absolute favorite thusfar, followed VERY closely by the SHP9500's....I will be adding a STAX SR-L300 in the near future, and that should complete my headphone selection: closed(ish), open, electrostatic...