The QP2R is just over half the size and about half the weight of the WM1Z. The Sony has at least double the battery life of the Questyle unit. You’ll get Bluetooth DAC and Bluetooth output capability from the Sony, also. Both can operate as USB DACs with the latest respective firmwares. Both are solidly built, but the rattling of the scroll-wheel and volume control on the Questyle make it feel less so - but the Sony is a brick (literally) and the most solid DAP build I’ve ever seen.
The Sony has 4x the on-board storage at 256 Gb, and with the latest microSDXC cards can mount a total of 768 Gb, versus at most 576 Gb for the Questyle.
The QP2R has a very basic interface, more like a classic iPod than the modern touch-screen stuff. Navigation is much slower (not due to UI lag or anything like that, it’s just a less efficient model). Though it has configuration options for just about everything you can think of (down to which direction the volume control uses for up vs. down).
The UI on the Sony is excellent, with very fluid, rapid and flexible navigation, a much better, brighter, sharper and larger screen.
I think the QP2R works best for starting and album or playlist and just listening. Once you start interacting with the unit the Sony units give a better experience.
Sound wise, in terms of raw signature, the QP2R is classic AKM4490 “Velvet Sound” but with an unusually dynamic delivery. Which makes it less neutral than the WM1A. Vs. the WM1Z, which has a richer, more liquid, delivery - especially in the mid-range … and a slight, general, sense of overall warmth - without resorting to low-end bloom/emphasis to get it. That is using both of the Sony units in their “Direct” mode, with none of their proprietary processing enabled.
The WM1Z, if you have an uncapped version, does a more convincing job driving more demanding loads, and exhibits less noise (almost imperceptible) with fussy multi-driver IEMs.
I much prefer the 4.4mm balanced connection on the WM1Z to the 2.5mm one on the Q2PR. I’ve seen far too many broken 2.5mm sockets in my time to want to use that connection on the go.
I have a personal preference, for everything except size and weight, for the WM1Z. I don’t know that I can say I think the difference in sound is worth the $2,000 difference in price (maybe $1,500 difference if both units are used), but as an overall package the WM1Z is my personal DAP of choice currently.