its actually pretty remarkable how different these three headphones sound from each other; the Z5 is like a much less warm grado without a soundstage, the Z6 is a downward slope and sounds extremely smooth and euphoric, and the Z7 is incredibly snappy and slammy with superclean bass and absurdly high detail retrieval
To elaborate further, the Z5 is actually noticably faster in attack than the other Z headphones, but at a price. As you go up, the driver becomes slower in attack but much faster in decay. Basically, take a modern Grado, get rid of the warmth and soundstage, and make it isolate like crazy. It has questionable distortion figures and mediocre extension in either end, and it's a little resonant and poorly controlled. It should theoretically also be the hardest to drive to perfection. It sounds a lot more "vintagey" than the other Z headphones, for sure. I'd say $150 is a major rip-off unless it's mint-in-box.