it's not a good idea to use xperia z for music the batt life is pretty bad
NEW Sony Walkman Z Series mini review!!! - Page 213
Gear mentioned in this thread:
Or any smartphone for that matter.
I recently gave up on using my Xperia S as music player because I couldn't make it through the day on one charge. I was getting 3-3.5 hours of screen time when it was doubling as my pmp, now I'm getting 4.5-5h.
The reason that the Walkman Z has such great sound quality is b/c of the "S-Master Pro MX" digital amplification. I'm doubt that the Xperia Z phones will feature the same digital amp though. With that said, the sound might be as good as the S & E series.
Japanese and North American units sound about the same. Is your Z a European unit? That may explain why.