I just did the test for you right now with an iPod and 'uncompressed' WAV files 16bit CD quality music: unamped they sound great, but amped they sound fantastic, simple as that. Without an amp you will be happy, but the clarity and definition that comes through when they're amped is a noticeable difference.
I hadn't listen to them for a couple of weeks, so just now when i listened to them unamped, i thought WOW that sounds great, but they will definitely need more volume if you like to listen to your music a bit louder than normal, but then i plugged in the FiiO E12 (classy amp!) and BANG! Now where talking.More detail, better instrument separation, more depth, better treble sound, better soundstage stereo imaging. Hope that helps.