Are you using any sound adjustment settings? I have the AK240 and the ZX2 and find that the ZX2 can vary greatly in sound quality due to these settings. Might be the source of such differing opinions. I have been using the ZX2 for over a week now and the biggest issue for me remains the "discharge hiss" that is present when starting the unit. Sony makes clear that the unit needs about 100hrs of burn-in play to reach its best but, even after a full week of 24/7 playing, the "discharge hiss" is still present.
On another note, I have run the ZX2 with the Audezee EL8, Noble K10, Shure 846 and JH Audio Layla and the ZX2 performs well from a volume/clarity perspective. However, I also tried all of these with a friend's PHA-3 in the mix and there was a significant improvement in SQ. Can't speak to the DAC differences or "cleanliness" of the amp but there is an obvious improved difference. Only downside was the size of the bundled package but this combo really gives the AK240/Hugo combo a serious run for the money.
PHA-3 ha one of the top dog DAC from ESS, and dual Texas instrument amplification chips with one each channeL while ZX2 has S-Master. If you have a chance to compare them. Please do so.
Regarding the burn-in from Sony, give the player 220 hours or around that mark for a complete burn-in.