I have a fiio E6 right now, and I really enjoy it's synergy with my budget koss headphones. The E6 adds a bit of high end energy which is generally quite nice in conjunction with a dark headphone like the portapro's.
I'm looking for an amp that has really good synergy with entry level grado's like the 60s, 80's or with the alessandro.
I also wouldn't mind improving on the battery run time of the E6. :)