Recently acquired a Philips Fidelio X1 as something I felt would be a compromise between my Denon D2000 abd Grado SR80i and they kind of are. Nice open airy sound, good bass response while being reasonably fast. Decent treble but definitely lacking in quantity compared to the other 2 headphones I mentioned. They're great, don't get me wrong but honestly too close to the Denons to justify keeping.
Of the IEMs I have the 2 that I like the most are my Triple Fi 10s and Senn. IE80s with my personal preference leaning toward the signature of the TF10 if that helps give you an idea of what I like. I listen to a lot of metal/rock/alternative but listen to everything from Radiohead/Massive attack to RIchard Bona, Bela Fleck (Jazz).I dig the response and quickness of the Grados and TF10s. I'm looking for something That provides detail while maintaining speed. I find that I'm not a basshead and prefer a tight controlled bass over quantity.
I primarily go from my MacBook Pro => itunes library through bitperfect=> Optical out to Fiio E17 => Grado SR80i, Denon D2000 or Philips X1.
I want something with good resolution, doesn't need to be bass heavy but prefer a brighter treble response as I believe I'm slowly going deaf due to my job. I'm considering the Sennheiser HD600/650s as I dig my IE80s but also dig the aggressive nature of my SR80s and may lean toward the RS2.
I know that "buy both" would be a legit answer but would like some input. I'll likely be selling the X1s as my Denons do pretty much the same thing but more to my liking.