I'll try to be a bit less subtle this time or I'll get myself into trouble. I'm 110% sure you already know this, but for anybody else who's itching to point out the blatantly obvious - QP1R's OS is Linux-based, while DX200 is Android 6-based. As you say, that means,
in theory, the UI/features of the DX200 are miles ahead. Note the use of italics
My main gripe with the DX200 is that despite its fancy hardware volume control and modern Android system it really isn't miles ahead of the QP1R in terms of user experience. At least, not yet. Yes, you can side-load some apps onto the DX200, but many won't work because not only is it missing the Play store, but it's also missing Google Play Services. If you're a purist and just using the device as a music player from the microSD (no wifi, no bluetooth, which the QP1R doesn't have anyway) there's not a whole lot of difference, and my preference in terms of ergonomics would actually go to the QP1R because track navigation and volume control are so much quicker and easier.
As for sound, that's a tough one to answer because it's going to depend on your headphones, what you're playing, what your preference are, etc. Let me throw out some controversial stuff here, so we at least have something to argue about. If you measure any of these modern DAPs though a loopback to your sound card, they'll all look ruler flat out to 20 kHz. I don't believe there are many people here that would be able to distinguish between the various types of roll-off past that point. The major sound differences - if there are any - are going to be as a result of the pairing with your headphones. Specifically, if your headphones 1) are very sensitive, 2) have very low-impedance, especially one that varies wildly with frequency, 3) have very high-impedance/low sensitivity and require a lot of power to drive. I've been listening to these two DAPs with the FLC 8S and SE846 - the latter of which definitely ticks the first two boxes. I hear a lower noise floor with the DX200, but the QP1R has more punch in the low-end. (And both these DAPs have Z-out < 0.2 Ohm) So, yes, I think SQ really is a toss-up. I think the best modern DACs (note I'm only talking about DAC, not amp here) are reaching the point where they're simply good enough. (The price of the 768 kHz sampling-rate Chord products are just a tax on stupidity IMHO. They're even a tax on stupidity for bats.) Now the DX200 amp is very solid, but so is the current-mode amp in the QP1R - it's one of the best DAP amps I've heard. I'm honestly not sure I could choose a winner in terms of SQ between the DX200 and QP1R. There are pros and cons to both, but the sonic differences between them are fairly subtle in any case. Folks that hear significant differences have usually not done proper SPL-matched blind A/B tests with a switch. You really need to. No, honestly, you do. This video explains why:
https://youtu.be/BYTlN6wjcvQ
I'll look forward to hearing your own comparisons when your DX200 arrives! (Please let us know what headphones you used to compare the two.)