I'm still trying to figure this out myself. I'll just kind of revise what I've said in previous threads and add to it here.
I own: Dt990 600 ohm, SR60 w/flats, RS1 w/buttons, HD25-1, Ksc 35, K701, K550, Amperior, Momentum, Sony MDR MA100, HD558, Samson 850 and R600, Aviator, and I've tried a lot of others. Didn't like the LCD 2 at the ALO booth at Canjam 2010. Thought the T1 was pretty good back then but not better than the RS-1 and surely not worth its price tag. I use either an Arcam 73 or Sansa clip zip as a source(even though I liked the Arcam 73 better than any source at the Can Jam that I plugged my RS1 into, it's basically retired now in favor of the clip). I really need an O2 amp. Then I'll have something that shouldn't be adding stuff to the sound, can travel with me, and should drive non-portable phones well.
What I think makes for great metal listening is to try and recreate the good parts of the live show experience. The energy and excitement of it all. That means I like to push things volume-wise. About as loud as I can get it without ear fatigue or pain or distorting the audio. Something that gives you a smooth audio rollercoaster that's also intense. Like if you could turn Batman The Ride into sound. If I'm tired out on a plane or somethin then I'd opt for something really smooth and clear since I'm looking to relax. The K701 with the Arcam was really great in terms of clarity and giving me a wide and deep soundstage, but it always sounded washed out through either a Darkvoice 332 or Heed canamp. And with that setup I sometimes had to really push the volume higher than I wanted because the 701 doesn't have the body to give some rock and Metal a rich, full, exciting sound.
I think this ibasso P2 can't handle what I want to do. It may also be adding too much bass into the mix. There isn't a ton of info on it. With the O2 I know what I'll be getting at least. Metal needs to sound exciting but it also needs something smooth that doesn't muddy up the sound. The HD558 can be the best of these most of the time, but it can also muddy up the sound and magnify any static on the recording. With the clip+558 and P2 Space Dye Vest from Dream Theater sounds like a bloated mess. That recording is already kind of messy and the clip/558/P2 sent it over the edge. No Rockbox eq could fix it. It might've been the 550 that brought out some of the dialogue out a bit more. Some of my older posts detail those other cans. I've only acquired the amperior and hd25 in the last few days.
The unique thing about the RS1 is that I think it has a wider, more open horizontal sound than any other headphone I can remember. It's not clamping onto your skull(which causes me fatigue even if it's not painful due to the weight and seal of stuff like Amperior or K550). This can be good and bad. With some recordings that are messy it gives them extra breathing room. When I put on a 1st press of Mercyful Fate Melissa, even if I add 8db of bass, it just doesn't give the song a full-bodied coherance. The Amperior is better there. The K550 does some albums marvelously well while it makes others unlistenable due to a cold harshness in the treble at times. As a general rule, 1st press cds made in the 80s work much better with good headphones than the Andy Sneap computerized monstrosities we've had to deal with for over a decade. I'm not sure how you make those sound good. I haven't been able to get Testament Dark Roots sounding acceptable through the clip at all. Even the flac files I made in Audacity with clipfix(which actually made Reinkaos sound better). However, Dark Roots somehow sounded ok on my Arcam-heed-K701 setup. Leprosy by Death is another album that's tough to get right. When I originally got it 15 years ago all I had was a bass boosted discman and MDR-V600 headphone.
With Metal I don't think it's so much a question of the genre sounding good as a whole on a certain headphone, it's more about the album. There's albums that sound awesome on certain phones and mediocre or horrid on others. Probably has to do with certain frequencies being amplified more. Spider's Lullabye by King Diamond is a horrid sounding album for the most part. It sounds limp on the Amperior. It lacks bass bigtime so maybe it sounded more lively on some of my other headphones because they emphasized certain high frequencies more.
The DT990 really gave the biggest impact of any of em. But it also lacked some clarity. I still recall how wow'd I felt hearing the slam on So Many Lies by Testament. I ended up preferring the airier sounds of the RS-1 and 701. Now if I could combine the two...
The extra treble emphasis on the RS-1 seems to bring out the voices more. Make them shoot out of the drivers. They're separated from the music pretty well, but not as totally as with the 701(and this is a good thing generally).
Metal can benefit tremendously from a wide and deep soundstage. There's always exceptions. One album that sucked on the 701 was Seasons in the Abyss. That headphone does a good job of isolating the vocals from the rest of the mix and placing them in the center but that album sounded too spread out and thin. It's already a kind of cold sounding album. I think horizontal width is much more important for metal than vertical(K550 and 701 are sometimes too vertical sounding to be ideal for metal, but get an A+ for movie scores). Guess I like something exciting, with great PRAT, that doesn't have frequencies bleeding into each other, gives the music room to breathe/is airy, has good bass impact, spreads out horizontally, and doesn't shoot treble spikes into your ears. The RS-1 sorta meets this but they really lack the kind of powerful bass you feel when you're walking up the stairs to enter House of Blues while a band like Priest or Testament is playing. The superaural Senns sound slightly congested compared to the open stuff so they're not really ideal. Very good though. 558 sometimes lacks clarity when I want it. If I was only listening to pre-1993 recordings this would be so much easier. After that so much Metal was recorded as loud as possible and not mixed very well. Then they got into all this computerized stuff and decided to make it even messier. My focus lately has been on closed cans so that I'm not stuck only listening to great phones in front of this monitor. Plus, you can get a lot of the best closed phones for $200 or less instead of $2000,
I tried a lot at Can jam before and wasn't into much of it. Walked away feeling like I still liked the RS-1 best, didn't want any of the source+amp combos I plugged it into, but that it might be cool to get the 701 and either an 880 or 990 at some point. I was hoping to like the Denon 2000/5000/7000 line but I immediately knew they weren't for me. I don't think the headphone world is looking to cater to people who listen to hard rock and metal. The mainstream stuff seems aimed at bass-obsessed kids and the audiophile stuff maybe more for people into genres like classical and jazz. The HD800 never worked for me as a rock or metal phone even after hearing it on several setups. Neither did the 650.
I wish headphone reviews would use some metal to test them. In some reviews I noticed comments where the reviewer stated they listened at lower volumes too. So there's a real lack of info on Metal as it relates to headphones aside from forum stuff. More often than not headphone reviews use tons of music I've never heard of (and I own thousands of albums across a lot of genres). For all the flack people give And Justice for all, I always liked the production. It's heavy and clear with good separation between the instruments. Uses a lot of horizontal space. Hopefully I will get to try some more phones. The UE 6000 at best buy sounded like it may be halfway decent with Metal. But that's with their setup and the phone set to active mode. There's a chance I may buy one soon either way. Maybe after I get my O2.
The last thing I'll note is that if you're not too picky, just get an SR-60 and order the grado flat pads from Todd. It'll give you a smooth, exciting, and wide sound that plays better direct out of a sansa clip than any of my other phones. It produces consistent results across metal, rock, dance, film scores, and pop. But it won't have the detail and other wow factors the more expensive phones do.