I tried a different source, my old Sony Walkman and had it on a radio station. Not bright or harsh at all, actually this headphone is just a whole lot of fun. Great sounding for pop and rock. Now I am wondering why my iPhone is a little hard sounding compared to my Sony Walkman. My iPhone files are even not MP3s, they are all uncompressed. Weird.
Radio cuts off at 14khz for FM and 10khz for AM. So there is less high frequency information. iPhone DAC amp is pretty good. Perfectly fine for the 7520. Give it some time. After owning these for a while I appreciate the 7520 detail and it is not harsh (but that could just b my preference)