I've seen several articles saying Sony Z4 will have a music edition. Smaller screen, two modes (Xperia and Walkman), maybe smaller battery, etc. I'm considering buying this phone so I don't have to bring another DAP for music. Does anyone know more detail about this phone? And which level of sound quality does it provide? FYI, now my portable DAP is Cowon P1.

Bump... Nobody knows?

No idea, but if http://www.androidheadlines.com/page/2 and http://www.ibtimes.co.uk/sony-xperia-z4-music-high-res-walkman-smartphone-pack-4in-screen-snapdragon-801-8mp-camera-1482835 are to be believed, the specs does look abit disappointing. If only it was the same as the normal Z4 in specs with added audio spec, I'd jump in without thinking.
 
With a lousier camera and processor however, does make me think twice as for a smart phone, it isn't exactly very future-proof.

Well, here it is.

http://www.androidauthority.com/sony-xperia-z4-officia-602463/

Interested in seeing how LDAC performs. Is it just Sony's version of APTX or is it supposed to be better?

I don't think Sony would be so foolish to put the S-Master HX in the Z4 for only $700. What would they do to their current ZX2 which retails for almost twice that and specs that aren't even half as good as the Z4.
 
From a business standpoint, I don't think it's gonna happen. Unless they drop the ZX-2 price to $400 or price the Z4 at $2000+
 
The Walkman is designed for music enthusiasts and people who want a dedicated player. The Z4 is designed to be a smartphone.