So lets compare how I see it. Mostly I do listen to techno/dance music, have used the same EQ settings on all of them, tested with IER-M9 (Kimber Kable).
NWZX707 vs. NWZX507 (burnt in I guess)
Its hard even to compare these two. ZX707 seems much better to me soundwise, it does sound richer, has much wider soundstage and overall feeling is just amazing compared to its precedor. Also the SW experience is very very good. As of the build quality, I think this is the best DAP Sony has made yet. Its just beautiful. Feels snug in my hand (I have small hands), but still its too heavy to carry around. For my walks, I guess I still will go for ZX507. I also got the original case, which is simply perfect. Even the ZX507 original case is way better than the bent crappy one for NWWM1AM2.
NWZX707 vs. NWWM1AM2 (burn in 44h)
Yes, NWM1AM2 has wider soundstage, overall it sounds better then NWZX707, but its not a big difference to my ears as ZX707 compared to ZX507. It seems to me that ZX707 has more bass, it slams better at some points. It gets really hard here comparing this two. It feels better to hold the ZX707 then the brick, so here, it really is hard to decide for which one to go as they both are not really to be taken for walks outside (I am not the guy putting stuff in my pockets, rather jacket).
I try to put it on a scale as I see it:
NWZX507 - 1
NWZX707 - 7
NWWM1AM2 - 10
(not meaning ZX507 is bad, but to point out the difference how i feel/see it)
If I would have to decide which one to keep, I would keep NWZX707. Sounds great, is snuggy, nice case - premium combo. Yes, NWWM1AM2 sounds better! And the NWW1AM2 with IER-M9 is my best Sony combo. I will get back to try with IER-Z1R.