If you want to experience high end sound you need to focus on three important things.
Edited by H20Fidelity - 12/24/13 at 1:11am
They must be of decent quality and a major part is them all working as one. (especially the headphone/source)
The most increase will always come from your headphone purchase however if you're spending $1000 on Sennheiser IE800 and running them with an iPhone and MP3 files there's no way you're going to extract their full potential and it's basically a waste of time, an earphone/headphone will only be as good as the weakest link or bottle neck. You may find yourself purchase IE800 and not like their signature at all, then you've just wasted almost $1000 in a puff of smoke.
The best way to progress in this hobby is start in the $100-$200 range and try a few different earphones, get a taste of different signatures such as bright/cool, dark/warm/ bassy, analytical, musical etc, it's not as easy as spending the most money and achieving the best sound, you have to think about the synergy of the source you're using with the earphone, the files, fit, tips, cables, it's more or less endless why people who get a taste for portable hifi end up never leaving because to me, (and I'm sure others) there is no end, there is no perfect end game rig. Some claim they found it, but then immunity to a signature kicks in, the brain becoming immune to the detail levels and technical ability starts craving for more. It really is an endless hobby and advisable to leave before you get dragged in.
If you want good sound, I can offer it and all for about $300 or at least provide some things to research, this would give you a starting point and something to focus on. If I was you I would cancel the IE800 purchase and look into this hybrid IEM which is really hot right now, Dunu DN-1000, ($200) also do some research on what hybrid IEM's are then, do more research on the audiophile player called Colorfly C3 ($100). Finally, start finding yourself some 16bit FLAC files (very important) and enjoy a clear, clean well separated and decently detailed set up on the go.
When you try that you can come back and tell us what you liked or disliked, start forming an opinion of what you like, dislike for future options. I can assure though the $300 you would spend will offer you good sound.