I have those exact two headphones. I've had the 555's for over a year and the SR80i's for about 2 weeks.
The 80i's are great for classic rock to me, they seem made specifically for that genre. The come with a miniplug. They sound decent straight from an iPod, but will leak out all kinds of sound being an open can. An amp of course makes them better, I've heard this is a key diff between these and the 60i's; an amp makes no diff on those. I like them for classic rock, but I can see why some people hate Grados.
The 555's excel at movies and games, very good soundstage. No contest here. These are more amp dependent. Mine, which are about 2 years old, have a 1/4 inch maxi plug, and a funky adapter, makes plugging these into an iPod real awkward, but don't sound very good straight from an iPod anyway, they need a bit more power. Still considered an open can, the design leaks much less sound out. They are substantially bigger, too. They don't fold at all. Very light and comfy. Surprising improvement amped, much more improved with amp than the 80's improve.
The Grado's.... hard to describe. First impression is they sound not so good. But then I realize I can understand lyrics for first time on song I've heard a hundred times, like on some old Who song. Hear bass guitar notes separate from rhythm guitar notes, separate from lead guitar notes. Yet soundstage is very narrow... Odd. But for movies & games, 555, not contest.
