I have not heard the Z1000, so I can not comment on its sound. But a lot of Japanese blogs / industry reviews / articles say the 7520 is the more "consumer" oriented version of the Z1000. They consider the Z1000 to be more for recording studios, and the 7520 to have more of a "fun" sound signature (I'm translating and therefor paraphrasing here). Most of them seem to think they are just different, and one is not necessarily better than the other.
According to some, Sony brought the Z1000 to the States, had some experts audition it, then implemented their input to create the 7520. That is why the 7520 was first introduced as the "overseas" version of the Z1000. At first the 7520 was only available in Japan as an import.
Again, all of this is according to what I've read.
I know you're just repeating what you read in another site, but I find their opinion strange. The 7520 has more even tonality so it should be more ideal for studios. It's the less colored of the two so that's weird IMO. Neither are very "fun" to be honest, and both show their studio monitoring roots to the core. They're both quite similar in a lot of ways. But Sony created the 7520 for studios after creating the Z1000 for consumers.
The Z1000 is just missing a lot of bass information, rolled off heavily starting at 100 hertz. It also has one of the most clausterphobic soundstaging I've ever heard from a headphone, and I normally don't give two schiits about soundstaging like other people.
Saying all this, I did love the Z1000 when I had it. Yeah I was sometimes bothered by the flaws mentioned above, but it was a beautifully built product that was so close to perfect, showed a lot of potential and promise with the LCP diaphram and magnesium build. When I heard the 7520 I had a big smile on my face cause I knew the engineers at Sony pretty much addressed a lot of the gripes I had against the Z1000. If people can find the Z1000 for cheaper (used or in some other country) then I say go for it and feel like you own 90% of the 7520 with better timbre.
Edited by M-13 - 12/29/13 at 9:42am