Quick impressions using an iPhone 4 with ZO and ZO2.
HE-300
When switching back and forth from ZO and ZO2 at lowest setting, I cannot really hear any difference in sound. With the ZO, when I click the vector switch a notch or two, there's a nice bump in bass. When using the ZO2, just a single click on the vector switch and the bass distorts. Neither the ZO or the ZO2 is a good match for the HE-300. Moving on to the next headphone.
I've been listening to the HE-300 and ZO2 for the past couple of hours using line-out and the distortion has gone away. I've been messing with the volume on the ZO2 and found a sweet spot somewhere near the middle. I can now turn the vector switch up a couple notches and it makes the HE-300's sound really nice. When listening to the 300's straight out of the iphone, the volume is really low and even when I have it cranked up full volume, it's weak and the potential of the 300's do not shine. Pairing it with the ZO2 and messing around with the volume level and it comes to life. I think the new volume feature might worth its weight. The way these headphones open up, the soundstage, tight bass, I think I'm digging the ZO2 quite a bit now.
PRO-900
I've been listening to the Pro-900 and ZO for a couple of weeks and they pair nicely at the lowest setting. When switching back and forth, I can tell the ZO2 just has more of an oomph. The bass seems a tad bit tighter, but I had to keep switching back and forth to really notice.
EX1000
The ZO and EX1000 were meant for each other. I've been loving this combination for months. Now to test the two. With an iem, I notice with the ZO2 there's more of an hiss than the original, but no static interference yet. During the testing, I would occasionally hear the ZO interfere but never with the ZO2. With the EX1000, I can notice the difference a bit more than the headphones. Everything is a little bigger, bass is tighter, more punchy, the soundstage opens up slightly more. I get the sense that ZO2 has more power than the original.
I really like the new coating they use and the LED is much brighter then the original. For owning both the ZO and ZO2, I cannot justify having both since the difference in sound really isn't a big jump. Now when I try it out with the ipod and lod, then I'm sure the ZO2 will be more to my liking.