LOL I've been asking myself the same thing. The fact that the HE-400 sounds so good makes me wonder if I'll be even happier if I splurge on something higher end. So I'm just trying to get a sense of how fellow HE-400 fans have reacted to more expensive orthos.
After reading this thread (http://www.head-fi.org/t/692229/he-400-vs-he-500-vs-he-4-comparison) and based on what people have said here, it seems like the HE-4 may have something to offer. Anyone have thoughts about owning the HE-4 in addition to the HE-400? Have any of you HE-400 fans bought an LCD-2 or compared the HE-400 to an Audeze?
If you are within your return period for the HE400, I personally think it would be more prudent to return them & getting the HE500 rather than x1 HE-400 + x1 HE-4. After all, you only have one set of ears.
If you are happy w/ the HE400s, I think you should just stick w/ it. No use wondering how greener the grass is on the other side when it takes double the price to jump over there if you are content with what you have now lol. It becomes a vicious cycle as well, because the higher-end your headphones, the more you feel obligated to spend on your amp/dac to get the best sound outta em.