Right now I have a pair of JVC HA-FX34 Marshmallows. I'm satisfied with them, but I'm looking to pick up a new/better pair. How much of a step up from the JVCs would the ER-6i be? Also, I know there are ER-6s. The 6i is described as "built for iPod" which is a bit of a deterrent for me...

I haven't opened them yet, they were a gift. I listen to bass heavy music pretty often, and some of the reviews I read said there wasn't nearly enough bass. In addition, a few of my friends have been telling me to purchase a pair of Sennheiser 555s. I do a lot of walking/busing so I'm...