I just got a pair of Pioneer SE-CL20U in-ear plugs and while I normally use my Koss PortaPro if/when I need phones (not often, since my Walkman broke and I don't usually like wearing phones), I was very surprised by the sound of these. When I first plugged them in, I tried listening to something in iTunes but even with the equalizer, it sounded like dog crap. I could swear I set it up so it saved everything as .wav or FLAC files but apparently, I need to check into that. I listened to some YouTube and it was a lot better, so I used my Dell Media Direct, which synchs to my music server with .wav files. The highs were good. Better than many plug-style phones and I refuse to use ear buds with the little foam pads. I never liked them and even with the clips, I won't use them. These, I like. The bass was far better than I expected and it actually provides a bit of a sense of impact. It's not like a kick drum hitting you in the chest, but for plug-style phones, it was deep, smooth and it's actually making me think about getting an iPod.
Granted, I don't listen to Rap or Hip Hop, but the bass was very good. The limiting factor with headphones is excursion and at high volumes, I suspect these will be no different but it was loud enough and I didn't hear any popping.