I checked these out at fry's. They have a demo with a narrator that shows off what they can do. The accuracy of instruments, separation, they run through various genres and he points out what to look for. I need to go back and listen some more. I had avoided them due to their look and a lack of info. Figured they must be overpriced junk. After hearing them I must say that what you guys have praised them for seems spot on. The demo plays some piano different ways so you really get a good sense of how the phones handle it. I didn't think they sounded too bass heavy or like they had fatiguing treble. I'd need to hear them some more, but my initial reaction is that they trounce the k550 and ue6000 that I own. I'd also say they beat the momentum too. Against the amperior it's a little difficult. I'd need to hear em with my own test tracks. The amperior is the only phone I own that really brings on the urge to dance and headbang when appropriate. It's also the only one that really gives proper weight to instruments in film scores. Direct out of my Sansa clip, I don't feel like the amperior is very congested. It has enough width and depth for film scores. Everything sounds bigger than on the 550 or UE6000. The big percussion elements on the carbon freeze music from empire strikes back hit with authority, clarity, and sound very accurate to me. I'm thinking the yamaha might pass that test. There's nothing worse than putting a phone on for metal and getting a sound that doesn't bring the guitars out or that doesn't lend the right bass and treble authority to a film score within an adequate soundstage. K550 has good treble and adequate soundstage for film scores but it lacks bass authority and body. It's better if you pair it with an amp that can add some bass coloration, but I'm trying to avoid buying amps to fix things I don't like in my phones. The things I didn't like about the pro 500 were the comfort and the sound you get from the materials. I notice that the material does play a part in how stuff sounds in these closed phones. The pads and the housing. The impacts on the amperior have this poppy sound, very round. With the UE6000 it sounds like the impact is hitting the plastic and metal it's made out of. The pro 500 impact sounds more like the UE6000. By impact I mean stuff like snare hits. I guess this happens with open phones too, like my RS-1 and the interaction with the wood. It's definitely different than my HF2 and it's metal housing.
The only changes I make with the sansa's sound is expanding the stereo width to 110% if I recall. I've switched my amp from an ibasso P2 to O2. The idea being to try and keep the source and amp neutralish and to find headphones I like without needing specific amps for em. When I go back to fry's I'm guessing I won't be able to plug my sansa in. Right now I barely use my 550, HD25, 558, or UE6000 so I doubt I'd be disappointed if I ditched them for the Yamaha. Last time I tested my wife's momentums it didn't do the metal or star wars music well amped or not. It did it ok, wasn't stellar. Just not what I was looking for.
Sounds like these Yamahas possess the things I like about the 550 and Amperiors based on what I've read and heard. Next I need to go to a local store and check out the M4U2.