I have both the PX100 and the Sr-60. The Sr-60 has the flat pads, wich give them the best sound. The comfy pads are comfier but the sound is a little veiled. Avoid the bowl pads for the Sr-60, they make the little Grado sound like cheap screeching earbuds!
So the next lines referr to PX100 vs flat-GradoSr60.
Senns PX100:
The PX100 have a very good sound, they are for me one of the best value headphones Sennheiser ever made, they are only a little bassy (NOT boomy), beacause they are equalized for a "young" listening (well, I am young, but I don't like too much bass...
). They are very detailed, the best thing are the voices and the extension in highs. Their sound is also quick, non resonant, and very pleasant to listen to. They are also extremely comfortable. Neverthless, they are inferior to the Grados...
Grado Sr-60:
For me Grados are the best headphone if we talk about sound quality. Period. And the Sr-60 is a truly Grado. Their sound is more equilibrated than the sound of the Px100, and their mids are Grado mids... liquid, warm and detailed at the same time. But the thing that make all Grado headphones shine is the harmonic analysis of the sound of instruments. It's not that the PX100 is bad, it's the Grados that is unbeatable!
Hope this review was helpful.
Bye
Andrea