Wow, I had to revisit the interview of Sony team to go through the efforts that they put inside the WM1Z, just to satisfy my curiosity as of why upgrading the internal wires can make it perform this way. Here is the link to his post
https://www.head-fi.org/f/threads/sony-nw-wm1z-owner-and-impressions.827575/page-2#post-13068909
What I found, important.
1/ New S-Master HX, 32 bits / 384 KHz...Native DSD into 11.2Mhz
2/ Super Low noise regulators
3/ Voltage to power supply is raised much higher than Zx2, going from 4V into 7V, and being regulated, purified into 5V
4/ Transistors are as large as found in Pha-3, due to how well they perform in sonic performances
5/ Resistors are Copper-goldplated terminals, which are found in high-end Desktop systems
6/ Braided structer of the internal wires helps reproduce better reverberations and reverbs
7/ Direct Line-Out was removed because the ground would have to be Directly connected into the Digital processing block, which increase the perceived noises. Completely eliminated this time.
Materials wise
8/ they did mention about special Capacitors and plugs sockets too, which to them did improve the performances, the 4.4mm due to more surfaces. The 4.4mm is awesome for portable uses from my opinions, it can fit in many different sizes of wires.
9/ Sony mentioned about OFC copper chassis as an exotic material for the chassis, and hence they tuned the WM1Z differently than WM1A.
The crazy thing is that .... Since I had moved on into the Stax world of SR009 + Kevin Gilmore Amp and Desktop DAC....I doubted the post modification WM1Z can impress me much as a portable setup out of Utopia as I am familiar with it performances in comparison to a full scale Stax system......I am proven wrong.
Once again, thank you NanaHolic for the awesome interview interpretation. It was such awesome works that you had done, which I enjoyed going through yet again