I would go with 99C against the other options. Makes a good pair with X5-3!
Under 500$ ?
Closed back, the 99C EQ'ed are probably the best bet.
Open back - maybe HD600 from senn.
I found which headphone is the best for metal
Had the chance to hear HE-1 today. Really really good with metal. Can do Dance Gavin Dance and Obscurcis Romancia really good.
I would only say this: I entered the store wearing 99C + FiiO X5-2, heard a ton of headphones and HE-1, then walked out wearing 99C + X5-2. I was able to enjoy music really good on X5-2 + 99C even after hearing all those expensive headphones
My 99C is EQ'ed and will sound similar to ie800 actually so there's this detail, but still. It is this good.
How is the impact?, he-1 is electroestatic, i think the electroestatic iems are the next way.. or not? haha