The way I see it... and the reason because I bought the PHA-2 is this: the F88x and the ZX1 are tremendous players by themselves, however, using an amp, the player is quite a bit irrelevant... as long as you can plug it on the amp.
Think about this scenario: Xperia Ultra , amazing 1080p screen but sound really lacks (there is hiss noise comming from the XBA-3, subtle, but noticeable whereas in the F886 there is none), then there is the F886... but sadly no real state screen (even though it looks nice). Then comes the PHA-2, that has all the goodies in SQ, but... it's just an amp. Now mix it with the Xperia Ultra, you just solved the lack on sound department (plus you can connect it to the PC... plus to the same walkman.... plus many more Android players), Also the Xperia Ultra has sdcard up to 64 GB, which is quite nice
(and also has the walkman app and the same sound enhancements as its non-cellular brethen)
Another plus that I found is that... well, for those that play games, you can emulate PSP and NDS games on it... my goodness, that thing has almost the same power as my laptop, which can do the same.