Closed vs. Open
 
Sennheiser vs. Denon.
 
I just picked up the Sennheiser and figured I'd give them a fair comparison to Denon's AH-D7000.  Up until the Denon's I was an open-can type of guy (I've had a few Grado in the past and the HD595 from Sennheiser).  I now wanted to get a decent can that was open to compliment the Denon's and boy was I in for a surprise after comparing them for the past hour just now.  I bought the HD 600 for mostly vocals and classical music but I found they excelled in other areas and disappointed in others.  Overall, I think both headphones are phenomenal and to have the option to flip between the two on a daily basis is a charm.  If you had to pick one though, it really depends on the genre of music that suits you most.  I like a little bit of everything but am not the jazz, acoustical guy but I tried to really put a wild variety of music to the test.
 
I consider myself a casual audiophile, meaning I'm not a huge stickler for every little detail.  I like to enjoy my music, not analyze it all day.  Therefore, my interpretations will be mostly in layman's terms but give you an idea of what's what.  I took samples from all the tracks listed as I have better things to do than to listen to basically 5 hours of music A-->B.    Without further saying here we go...
 
 
The Headphones:
Denon AH-D7000 (stock)
Sennhesier HD600 (with HD650 cabling...newer drivers)
 
AMP/DAC
Audio-GD FUN (Earth OPAMP for warmer sound)
 
Source
Windows 7 PC with Foobar2000 (WASAPI) output via coaxial..
 
DISCLAIMER:  When I played any tracks with the Sennheiser HD600, I did EQ up the bass just a bit at 55Hz and 70Hz a few decibels as I saw online the frequency response rolls off on the low end.  This made the bass very comparable in power to the AH-D7000.  It did make the HD600 even harder to drive because to avoid distortion I did have to lower the rest of the curve.  It is a NIGHT & DAY difference on the HD600 for the better as it brings out the bass more w/o drowning out anything else. 
 
Tracks I think the Sennheiser HD 600 are better at...

Frank Sinatra - Come Fly With Me
Better soundstage on the Sennheiser.  Denon's are more in your face but with a smaller sound stage, things sound close to you.  Both project his voice phenomenally with great detail.  Cymbals are a bit more present on the Denon's maybe because of the closer sound stage.

Enya - Only Time
Both sound amazing, just the Sennheiser hides the hiss in the track more

Chris Daughtry - Used To
Both sound amazing, but Sennheiser's vocals just put you there.

Leann Rimes - How do I Live
Denon's are missing something on this track I just can't place it.  It doesn't have the bass guitar details.  It lacks texture and detail in comparison to the HD600.  Instruments basically take a step back on the Denon's with the vocals being more forward.  It's not a bad sound on the Denon, just doesn't feel the same.  Sennheiser puts a better sound overall on this track.  I'm not a fan of this genre but I found myself listening to the track a second time just for fun. 

Queen - Play the Game
Both are rather equal on this track, larger sound stage on the HD600

Red Hot Chili Peppers - Parallel Universe
Denon's have a better bass hit, but something just doesn't sound right about the sound.  It's more in your face but something is artificial about it.  The Sennheiser just sounds like a nice mix of all the instruments.  Vocals are more crisp.

Usher - Hey Daddy
The surprise track for a rap song with lots of bass, the Denon's have killer bass, but sounds strained.  On the flip side, his voice is just amazing on the Denon.  It's right in your face.   The Sennheiser bass is not as strong but sounds more focused.  Voice is very natural sounding and not so much in your face.


Songs I feel sound better on the Denon AH-D7000

Red Hot Chili Peppers - Otherside
Surprising that I had the other RHCP song listed as better on the HD600 that I found a different track by the same artist on the same album to be considerably better on the Denon's.  You can just feel the vocals and bass guitar in this one. 

Massive Attack - Unfinished Sympathy,
Massive Attack - Angel
Massive Attack - Teardrop
Massive Attack - Inertia Creeps
Clustering all these 4 together, these are the songs if you like bass is where I have yet to find a headphone to match the D7000 for sheer volume.  I was surprised at how well the HD600 can attempt to keep up (esp. on Angel's intro).  The Sennheiser's don't sound bad at all on these 4 songs, it's just not the same for visceral poundings.  Denon's make it feel like you have a subwoofer attached to your head.

Sixx:A.M. - Life Is Beautiful (Intro)
Both sound amazing, the cymbals are a bit better on the Denon's.  Guitar is equally quick on both headphones.  Sennheiser removes the hiss well from the track when you want to play it loud.  Eitherway, Denon's are better.

Eagles - Hotel California (Live)
This is the song I demo the Denon's with because the drum kicks are just ridiculous.  The Sennheisers are lush on this song but sorry, can't compete.  You just close your eyes and get sucked in on the Denon's.  

Bach - Toccata & Fugue in D Minor
Denon captures the low end organ sounds better
Sennheiser - have a more realistic sound but Denon's more enjoyable
I'm starting to see that "distant sound" everyone says Sennheiser has with putting you a few rows back.  
Surprising as I bought the HD600 for classical.

Andrew Rayel - Aether
Denon's just have a more sensational sound and better bass.  The Sennheiser's are boring and it feels like "just another song."

Armin van Buuren - Virtual Friend
Everyone's told me this song kicks the Denon's butt in when it comes to exposing tons of sibilance.  Yup, Sennheiser beats them out here for the intro vocals but after that, I'll take the Denon's once the beat kicks in.

Green Day - The Static Age (Intro Drum sequence)
Lots of fast hitting drums puts the speed of the cans for a test.  Denon wins this one hands down...much cleaner and able to keep pace.  Bass is strained on the HD600 while Denon is just effortless.
 

These songs sound amazing on either the HD600 or the AH-D7000.  Both have their pros and cons but none stands out as the clear winner in my opinion...
 
Metallica - Enter Sandman (intro)
Simply wow on this track, unfortunate part is that HD600 can reveal a bad recording.  I started demo'ing the track and realized real fast I accidentally loaded an MP3 copy of this instead of a PCM rip.  Switching it back over I got rid of the "swish swish" cymbal sounds.  These things really are revealing.  Denon's are great on this, but you miss the texture of the guitar.  When the drums start kicking though, they hit harder on the Denon's and feel more alive.  It's really a draw.
 
Taylor Swift - Love Story
Much wider sound stage but besides that, both sound very impressive.  Great vocals, great guitar, great treble. 
 
Kings of Leon - Use Somebody
Instrument wise - Denon's are better, vocals wise - Sennheiser is better.  Honestly though, I'm being picky on this track to find a difference they are really close.  Just an awesome slow modern rock song to show off a pair of high quality headphones.
 
Pink Floyd - Another Brick in the Wall (Part I)
In comparison to the HD600, you can hear more artifact and hiss in the track on the Denon's.  The vocals sound more artificial on the Denon's, but the guitar is more visceral on the Denon's.  Really a draw. 
 
 
 
CONCLUSION
I'm glad I bought the HD600.  It put a different perspective on the music I listen to as I mostly was using the Denon's since I got them.  I'm a casual audiophile but am noticing differences on these songs.  Both are an awesome headphone and glad to add both to my collection.  I'll admit, during some of my testings I got confused as to which headphone I had on my head while reviewing they were that close on some songs.  Thanks for reading.

very interesting.  nice comparison!

NOsferatu...nice review. Obviously you put a lot of time, thought and effort into it.
You now own a couple of truly great cans. Congrats.

Nice music selection! Pretty much the kind of music I listen to.
 
Also like your review format, just describing what songs you think sound best on a certain headphone is a very honest way of doing a review.

Thanks guys.  Like I said it was a lot of tracks so I couldn't go from start to finish on every song.  I just hit the same key parts in each song and tired to just forget about what headphone I was listening to.  Adding a little bass via EQ on the HD600 made a substantial improvement of the sound without hurting the rest of the frequency spectrum. 
 
I did it for fun the same settings on the Denon's and the bass just became too much...and that's a lot for me to say considering I come from the "there's no such thing as too much bass" camp. 
 
 
For regular listening sessions, I'm just using whichever headphone I feel like using based on mood. 

i guess without the EQ, there is a CLEAR winner....? 
 

well yes & no...if I want the HD600 to keep up with the D7000 for songs where the low end is important then absolutely.  The HD600 do have a decent amount of bass w/o EQ but I see you have a D2000 so you know where I'm coming from with a D7000 when I'm used to hearing the low end on a pair of cans.    Most of the songs I listed that sound better on the HD600 would all sound better on it still w/o EQ'ing...with the exception of maybe rap where you need that low end.

Nicely written review, good idea to comment on the track you listened to. Sounds like that's two great complementary cans you've got there. 

Nice job with your impressions!