Spent about an hour at Sony Building in Ginza doing an A/B between the ZX2 and my AK240 using my Noble K10. I also had my A17 on hand, and did a short A/B between the A17/PHA-3 setup and the ZX2/PHA-3 they had on display.
AK240/ZX2 - To be fair, I used the balanced output on the AK240, and used an adapter (same cable) to listen to the ZX2. The tracks used for the comparison included Norah Jones, Daft Punk, Michael Jackson and a couple of jazz tracks (Dave Brubeck and Miles Davis). To make the long story short, the ZX2 was quite impressive. The overall presentation, including depth and width of the soundstage, balance across all frequencies and the level of detail, actually was leaps beyond the ZX1 or the X5, both of which I used to own, and even compared with the AK240, the ZX2 held up on its own. The AK240 had a slight advantage in the treble presentation and soundstage depth, but I actually preferred - hate to admit this - the bass impact of the Sony DAP. On the Daft Punk track, I clearly preferred the Sony over the AK240, as there was just a lot more sparkle and force wih the Sony...BTW, My AK240 is a plain vanilla one, and I am sure that the owners of RWAK mods have nothing to worry about, based on my limited experience with the mods. On jazz tracks, I still preferred the AK240 over the ZX2. I felt that the AK240 did a better job of conveying the sense of space and also a tiny-bit better on the detail/separation department.
A17/PHA-3 vs. ZX2/PHA-3
Only allocated a limited amount of time for this, mainly because I actually didn't notice any major difference between the two setups when I started listening. I guess it makes sense given that the DAPs were basically feeding digital signal to the PHA-3. The display setup had a Sony Z7 headphones with stock balanced cable for PHA-3, and I didn't bother swapping it out with my K10s.
Would I buy the ZX2? As an AK240 owner, it is just difficult to justify the additional cash outlay, or switching over completely. The sound quality of the ZX2 really surprised me, and the overall sound signature is different enough from the AK240, so it is really tempting... If I did not have the AK240, I would have a tough time choosing between the ZX2 and the AK240, as it may be difficult to justify the price difference between the two DAPs on sound quality alone... If you already have the A17 and PHA-3, and you primarily listen via the PHA-3, it also doesn't make too much sense to buy the ZX2 unless you do or die with DSD playback functionality... The upgrade should be a no brainer for the ZX1 owners, and anyone starting from a clean slate looking for a high-end DAP should definitely give the ZX2 a listen.