Kinda off topic here, but I think this is a good place to share because there seems to be many budding audiophiles on here.
So I brought a friend from work over to my place to try out my headphones. He has tried my portable KEF M500 at work before and compared it to the company supplied headphones he's using, some cheap $5 plastic Logitech headphones with mic. One of those that have two plugs, one for sound, one for mic. At the time, he said he couldn't hear the difference between my KEF and the Logitech. So last night, I had him over to try out my Sennheiser HD800. I had him bring along those Logitech for comparison as well. I had the Logitech running straight from my computer headphone port, and the HD800 running through my full setup (DC-1 DAC -> Quickie preamp -> Crack amp -> HD800). When he heard the same song through both, he told me that he couldn't really hear a difference! Then I had him tell me a song he knows very well, and I downloaded a song that he listens to more than 10 times a day. This time around you could see on his face when listening through the HD800 he was noticing a difference. And did he ever notice a difference! After the song he told me he never realized there were all these other instruments playing in the background, how he could hear the singer's breath in between lines, and how before the bass was just a nasty jarring sound before (due to distortions at high volumes), and now he could actually tell it's bass and it doesn't hurt his ears at all. He realized how much he's been missing out. You really have to listen to something you know well to hear these differences.
I had him try my Hifiman HE-500 next. By audiophile standards, these do not provide as much detail as the HD800, but the bass is more impactful because they are planar magnetics. Anyways, like I expected, he could not tell that it was worse in detailing compared to the HD800, but did feel the more visceral bass, and he actually liked the HE-500 better than the HD800. This was expected because while the difference between some cheap $5 headphones and a $150 headphone like the M50 is vast, diminishing marginal returns hit fast and hard, and for someone without trained ears, he could not hear a difference between $600 and $1500 headphones, so the HE-500 and HD800 sounded the same in terms of details, but he could feel planar bass because planar bass is like no other. I told him he should just get some headphones like the HD598 for $200 and he'll have 95%* of the HD800.
*This is 95% figure is adjusted to my friend's hearing ability and currently untrained ears. I'm sure if he had both to compare, he wouldn't be able to tell too much a difference, if at all. On the other hand, having more trained ears from this hobby, and having owned and recently heard the HD598, I personally would say the HD598 is like 40% of the HD800. You'll find your ears becoming spoiled as you listen to better sound and your old crappy headphones sound far worse than you remember them to.