So, I bought some Sennheiser 595's and 598's along with 555's. I kinda want to stick with the 555's, as I won't be too terribly upset losing those and I can return the 595's and 598's to Amazon without losing any money. I will be using these with my iphone 4, I've heard everything is better with an amp. Does anyone have any suggestions for an amp that small enough to attach to to my iphone? I really don't want to buy an amp that is the size of my fios DVR, since I've seen amps that are able to attach to the back of an ios device (e.g. my iphone), but I want to enjoy better sound. Thoughts?