Here you go:
You already have a good headphone amp which will allow you to pick out which is your favorite set of cans.
Pick your favorite pair, keep them and keep the Grados for your PC, sell the rest.
Then go off in a different direction and get this:
http://www.ebay.com/itm/STAX-SR-407-CLASSIC-Electrostatic-Earspeakers-/321057161907?pt=US_Headphones&hash=item4ac07f82b3
and this
http://wooaudio.com/products/wee.html
and you'll be done thinking about buying headphones.
This will give you two totally different presentations to the music, both of which will rival speakers in the 5-10 thousand dollar range.
Note: the Woo Wee is only the adaptor unit for the electrostatic headphones, you will need to hook it up to an integrated amp, receiver or amp/preamp. Whatever sound quality you put into it is what you'll get out. If your amp/preamp bites so will the sound.
Stax earspeakers are very revealing so consider yourself forwarned!