What's your budget? I just invested in some Audeze LCD-2s with a Schiit Lyr amp and some Soviet era tubes to replace the stock ones (recommended by a metaller on head fi forums)
The sound blows away all my previous listening experiences but it is quite pricey. But if you have the cash and you are into your music as much as I am into mine I would undoubtedly say it's worth every cent.
For something cheaper, I'd recommend the Sennheiser HD 595s. Those were my go to headphones for about 5 years before just now upgrading to the Audeze headphones. Very good for their price IMO.
The LCD-2 sound is very warm, full and lush (what I wanted as opposed to something bright and thin sounding). Before I upgraded the tubes my only problem with the guitar sound was that it sounded too "laid back", with not enough bite/crunch. With the tubes I just installed though it's perfect. Hard hitting, but not fatiguing at all.
I tried some "extra bass" IEMs before getting to the Audezes and wasn't really happy with the sound. Too boomy for metal. Very good for electronica though. The Audezes have a very deep hard hitting sound (with these tubes), and awesome bass extension but do not sound boomy.
EDIT: Check out the Head Fi forums, there's loads of people on there and plenty of them listen to metal so they will definitely be able to help you. I myself am brand new to the whole hifi scene.
