I recently acquired a Yamaha Pro 400, and I would go with that for closed and AKG 701 for open. They both have a sort of big screen tv equivalent sound, meaning that they enlarge most details while having a lot of width and depth. The 701 is a little faster and more immediate. The 400 can have a lot of sub bass. It's weird because a lot of metal sounds full and clear, but something like Fight-War of Words original pressing from 1993 will have its drums create tons of sub bass. It doesn't end up distorting, it's just different to listen to a headphone that is capable of recreating the power of drums like that. I just eq the bass down a little with my Sansa clip if I want it to sound more regular. For an amp, I use O2. I had been using a Darkvoice 332 and Heed Canamp, but I feel the O2 provides more transparent, better results. The 400 gets louder than other phones I have directly off the Sansa Clip. In my experience, I prefer closed headphones for Metal due to the smoothness and bass. Open phones tend to let a lot of the headbanging bass escape while magnifying static. The K701 seems to minimize that while also providing the necessary urgency in the sound to make metal sound exciting. Just try the original cd of Painkiller to see what I mean.
I'll list other phones I own and comment about using them with Metal:
RS-1 with buttons-Too much treble
HD558: Too much static
K550-Pleasant, but very light and bright
UE6000: Very nice tonality, but has almost no treble energy.
DT 990 600 ohms: Very nice tonality, can be a bit too forward and fatiguing unless I use it with the Darkvoice and Arcam 73
Amperior: Nice tonality, good bass and weight to the sound, but can be a bit forward and fatiguing
HD25-1: Could sound fuller
SR-60: Less fatiguing than RS-1, but not as resolving or natural
Momentum: Good technically, but kind of muddy sounding at times.
Aviator: Too forward.
HF2: more body and bass than RS-1, but now the treble energy is a little low.
AKG 240: owned this and may buy another. This was like a muddier 701 that had better bass. I never got to try it with a Sansa Clip or O2. The amps and sources I was using it with were a bit colored, so I'm hoping it has better results with the more neutral Sansa and O2. This is definitely worth considering.
AKG K44: too muddy
Samson 850: Sort of like an AKG 240 with less bass and more open sound. Haven't tried it with Sansa clip.
Samson 600: Similar to 850, but more Gradoish soundstage. Need to try it with my Sansa as well.
I've heard many other phones like Sr-009, Abyss, T1, HD 800, HD 650, RS2, SR 225, SR325, Yamaha 500&300, the new Denons, LCD 2&3, some of the less expensive stax, M50, DT770, whatever else Best Buy has for demo, various Ultrasones at CanJam 2010, various other Senns, Phiaton various, the old Denon 2000-7000 line, a few audio technica, and probably others between all the meets and stores I've been to.
There really isn't a perfect metal headphone. So much metal is harsh-sounding on phones for one reason or another. Testament-Dark Roots is unlistenable on a lot of phones, but the 701 works pretty well for it. Right now you can buy a Yamaha 400 from Amazon for $150 used. It's possible to acquire a 701 for around that price too sometimes. I haven't tried the 400 with an amp yet. It seems to work well with both old an new metal. After the 400 and 701, I would go with a K550 or Amperior as my next choices.