Pros: Excellent bass, easy listening/no fatigue, Large soundstage width, pricing, build quality
Cons: Timbre is lacking, heavy, ringing, detail
I am currently using a loaner pair of HE-500's and thought I'd give my thoughts on the headphones and how they compare to my current pair I was planning on upgrading (Sennhesier HD 600). Keep in mind these are all subjective thoughts, what may be a con for me can be a pro for you based on your preferences. I loaned a pair from The Cable Company, http://www.thecableco.com/Product/NEW-Headphone-Lending-Library.
Bass: The HE-500 has some of the best bass I have ever heard on any headphone and absolutely dominates the HD600. There is no mid-bass hump that I hear present in most headphones, the sub-bass has great extension and can really give you a nice rumble when the song calls for it. The bass is very dynamic and suits any genre. It is well controlled, fast, and textured when listening to rock and metal, precise and natural when listening to jazz and classical, and can deliver a nice amount of thump when listening to rap, trap, and dubstep.
Soundstage width: Contrary to another review I read, I found the HE-500 to have much better width than the HD600, the HD600 sounds narrow versus the HE-500, this was very evident when listening to Miles Davis. The drums and trumpets sound more outwards towards the left and right, but not so much so that I find myself losing excitement or so that the music seems distant.
Little Fatigue: Once I got used to the clamping force and heavy weight of the HE-500, I'm able to listen to them for hours without any fatigue. The laid back lower treble makes these very easy on the ears. The upper part of the treble has good extension, hi hats/cymbals/etc have a nice sparkle without sounding overdone and ear piercing, which was a big problem I had with the HE-400.
Ringing: For some reason, If a high frequency note is played for a continuous period of time, the HE-500 produces a strange ringing effect, even more so than the HD600. It's kind of annoying and hurts my ears. Listen to a opera singer holding a note for a long time, or a trumpet being held on a single high tone, you will see what I mean.
Timbre: I find that drums, trumpets, the piano, and guitar sound more true to life on the HD600. I originally thought this was because I wasn't used to the planar drivers on the HE-500, so I listened to them continuously for a extended period of time, then switched to the 600. I still found timbre to be much, much better when doing this and also during a/b testing.
Lacks detail: Due to the laid back lower treble and wide soundstage, I find the HE-500 produces less detail than the HD600. I can hear more subtle details, like recording errors, static noise, and reverberation of instruments. This is because of the brighter lower treble on the 600 and the more intimate presentation.
Smoothness: The HE-500 is a smooth headphone, but the HD600 is even better in this regard. I find less peaks in the HD600s frequency response, music sounds much more coherent and neutral without any extra glare/brightness being added. Everything sounds like it flows together naturally with the 600, while the 500 breaks the flow with ringing and a light glare
Song Tests (Done with pleather pads, Schiit Magni & Modi, FLAC/ 320kb MP3s)
Bitches Brew, Miles Davis, Jazz
500: Soundstage is much larger in width, drums extend more outwards towards the left and right. Timbre sounds less realistic on the drums and trumpets, however, the bass is more present in the song.
600: More intimate and exciting sound, drums don't extend outwards left/right as much as 500, however the drums and trumpet sound more true to life, timbre is much more accurate, the bass is lacking just slightly versus the 500.
Passed Me By, Andy Stott, Electronic
500: Bass extends all the way down and has a much stronger impact, ambiance of the song surrounds my head and sounds as if it's warping/surrounding around me.
600: The very low sub-bass is almost ignored, much less impact, ambiance of the song is more intimate and lacks the "surround sound" effect I felt with the HE-500.
Teardrop, Massive Attack, Trip Hop
500: Presentation is larger, drums have more of a "pop/snap" and the guitar sounds livelier vs the 600, but timbre is still stronger on the 600. Mid-bass is less excessive on the song.
600: Presentation of the song is more intimate (sounds more in my head), the guitar and drums have more accurate timbre, Vocals are smoother and have less sibilance and peaks.
Song Of Life (Nick Warren Remix), Leftfield, Techno/House
500: Bass is quicker and has more impact, drums/cymbals have more sparkle and shimmer. In general, this song sounds much more lively and energetic vs the 600.
600: Bass is less present and lacks the impact and speed of the 500. Drums/cymbals lack the sparkle/shimmer of the 500. In simple terms, this song sounds more smooth and is easier to listen to on the 600.
Warrior Concerto, Glitch Mob, Electronic
500: Clearer and more open vs the 600. Bass has a strong rumble (1:50-2:10), much better imaging and separation.
600: Sounds congested, all of the instrumentation/soundfx sounds too close without enough separation, bass is lacking impact (1:50-2:10 in the song)
Both are truly great headphones, but you may favor one over another based on your tastes. I think the HE-500 and HD600 compliment each other well. I often find myself grabbing the HD600 for jazz, classical, and instrumentals for the beautiful timbre and intimacy. Then I switch over to HE-500 for dubstep, trap, rap, and rock/metal because of the bass, more shimmery upper treble, and speed. Both are driven by my Schiit gear with ease, I find both headphones can be driven to ear damaging levels with the Magni & Modi. However, the HE-500 is more dependent on amping. The HD600 sounds good out of my Nexus 4/computer, but plugging in the HE-500 to a portable source leads to dull dynamic range with little bass impact.
That about sums up my thoughts, hope you enjoyed reading my review!