I have heard that the sound signature of the 1Z does differ from the ZX300 and the 1A, but if I'm not mistaken the general consensus is that it still sounds better, so if I were to upgrade in the future the Z would be a logical choice, but as I mentioned the price tag and weight may turn me off a little. If I were to go with anything else I might choose the SE100 or the SP1000M, but one still isn't portable friendly (SE, large size), while the other is still quite pricey (SP, $2399), not to mention the completely different brand that I'm not familiar with.