I bought a EX600 a month ago and was pleasantly surprised by its sound, but the sharp treble has always sorta kept me on my toes at times. Upon finish reading this thread and discovered that the 7550s might be a more suitable pair of phones for me, so I ordered one.
Two days ago I received my pair of 7550 and have burned them for about 48 hours.
Out of the box, they already have the EX600s beat hands down. Like many members have mentioned before, they share a very similar sound signature, but the little differences are definitely noticeable.
Treble: This is where the biggest difference between 7550 and EX600 lies. EX600 has a very 'exciting' treble with nice extension, but on several tracks they make me twitch with the sharp treble. Sometimes they could also sound a bit digital and unnatural. 7550, on the other hand, retains that great extension, but there is absolutely no peak or sibilance at all. I've thrown all of my sibiliant tracks at it and I've never heard it once. It's super smooth and super relaxing to my ears. LOVE it.
Mids: 7550 mids are definitely more forward than EX600. Not a night and day difference, but just makes everything sound more 'right'. Vocals are more upfront, so they no longer blend into the instruments, which sometimes happens with EX600. It makes cello sound stellar, warm and engulfing.
Bass: More emphasis on the bass with 7550. The bass lines are slightly more defined and easier to pick out for complex jazz pieces.
Soundstage: 7550 is a tiny bit wider than EX600, but quite a bit deeper. Instrument separation is better and I hear more air around instruments, especially for strings. Overall 7550 sounds more 3 dimensional.
Details: Being a studio monitor, 7550 obviously has a TON of details, but interestingly the details don't stop me from enjoying the music, they don't scream in my face, I can
choose to hear them if I want to.
These little changes add up and just makes 7550 that much more musical and realistic sounding to my ears compared to EX600. It's kinda hard to imagine how much the EX1000 can improve over the 7550. I'm actually quite awestruck but how good the 7550 is, especially coming from ES3X/SE535/HD800. Right now I actually prefer the sound signature of the 7550 to any of my other headphones and even makes me want to sell the SE535.
My only gripe with 7550 is the 1.6m cable, it's just way too long for me, but that's just nitpicking