The graph above shows the frequency response of three headphones I own (HD 518, AD700, and Ortofon O-one) and of one I do not (HD 558). As you can see, the HD 518 is the bassiest of all; this I can confirm from listening. The 518 is clearly much closer to the HD 558 than to the other two. I will have to defer to KJag as to the sound difference between the 518 and the 558, because I believe he has both. As stated before, it has been claimed (with some photographic evidence) that the 518, the 558, and the 598 share the same driver.
Great advice thanks guys i contacted amazon and they have told me i can use both headphones and if not satisfied can send one or even both back for full refund so going to order the 518 and 558 tomorrow. Quick question, would it help if i was to purchase the fiio e06 would i get noticable difference in quality with either of these headphones and it states that it has equalizer will that increase bass more than if i was to connect to my smartphone which already has equalizer? And do i need the amp if connecting to my tv with headphone jack? Lastly i read somewhere that with amp you can connect to tv so sound comes out of tv speakers and headphones simultaneously because atm connecting anything to headphone jack stops speaker sound. Also i know the eo6 is just a budget amp but budget is what i can afford at the moment lol thanks guys.