Following up from my
first post on the Onkyo DPX1 yesterday ... including a picture (for provenance, mostly):

Summary:
If you're looking at the DPX1 to use as a DAP, driving headphones directly from one of its two outputs, playing files from local storage using the built-in "Music" application, then it is an excellent little device with very high sound quality, solid battery life*, a fast and fluid user experience (at least with the 400+GB/12,000 files I tested with).
Used this way, via it's internal DAC and headphone amp, the sound quality is superb and easily bests the native outputs from an iPhone 6S (not surprising, really), my AK120 and an AK240 I was playing with at work yesterday.
So, as a straightforward DAP used as-is, I think it's well worth consideration and is unlikely to disappoint. I'd recommended it, happily, for that use case - with the caveat that the headphone sockets really do seem rather insubstantial.
However, if you want to use Bluetooth headphones or an external DAC or wanting it to stream TIDAL or Spotify, or play music via other player applications on Android (via Google Play), then there are some significant issues you should be aware of.
Bluetooth:
I won't belabor the point; you can read my original post for more details
here, but in short, beyond the normal Android fussiness with Bluetooth, this thing exhibits continuous, repeatable, drop outs in playback (tested with several different Bluetooth headphones now, including Blue-Buds X and Momentum 2.0 Wireless Over-Ear). This issue is bad enough that I cannot listen to music via Bluetooth with the DPX1 in either my pant or shirt pockets (nor when I tried just holding it in my hand). Even in my shirt breast pocket, at a range of about a foot, I get reduced audio quality and just turning my head results in the connection dropping completely until I turn it back.
It worked fine with the DPX1 on a desk with unobstructed line of sight to the headphone receiver, but range was maybe a third (at best) what I see from my iPhone, before it would start dropping out.
Distortion w/ Third Party Music Players:
Using third party music players results in audible distortion in quiet portions of the music. This is most notable during the fade-out (or fade-in) of a track, but it's come up in classical pieces with quiet passages and in some contemporary music where the artists drops to a whisper for part of a song (etc.). It's quite obvious and not something you're likely to miss and seriously spoils the viability of this player for use with third party players (the major draw, as I see it, for having an Android based DAP in the first place).
I've tested this with the standard TIDAL, Spotify, Amazon Music and Apple Music applications, all playing through the
internal DAC/amp, and the distortion is present in all cases. It didn't matter if I was streaming the file, or playing a locally cached copy.
I did not hear this same distortion when playing those applications via an external DAC, although that output is still subject to Android's native re-sampling.
Using External DACs:
This works fine, but unless you use something like USB Audio Player Pro, you're still subject to Android's native re-sampling which I can't say does sound quality any favors. If you do opt to use a player that bypasses the Android Audio subsystem then you'll get to enjoy the issues I found (see my original post) in switching between players and getting them to release/recognize the DAC.
Most of my testing here was using a Chord Mojo. I would say that the Mojo yields higher quality output that the built-in DAC/amp, and drives more challenging headphones with more authority.
One of my hopes was to use the DPX1 as a transport with the Mojo for when not having to travel light (and when traveling light to use
just the DPX1). I found the messing around that was periodically necessary to switch between music players, with the hard-crashes (occasionally requiring a power-off/on cycle), meant I was sometimes spending several minutes getting my music playing ... often at the cost of as much as 10% battery life*!
Avoiding Android's Up-sampling:
If you're using an external DAC, you can do this with UAPP, and you'll
want to as there is a quite noticeable improvement when you bypass it. UAPP can stream directly from TIDAL now, and while the interface isn't as nice as the standard TIDAL client, it's worth it from a quality perspective.
Battery Life:
Battery life was excellent when playing music with the built-in player application, and even with streaming TIDAL over a solid WiFi connection I was seeing about 5-6% depletion per hour (sometimes as much as 10% if I was using more demanding headphones). The claimed 16 hours in standalone mode is easily attained - though that only works with the built-in player also.
*However, doing anything with the device other than playing music causes the battery level to drop very rapidly. In one case I spent about 5 minutes trying to get the player to release my external DAC from the built-in player and make it available for UAPP, and by the time I'd done that I'd lost 10% of my battery.
Final Thoughts:
Great as a standalone DAP, used as-is, with no third-party apps, no Bluetooth and no external DAC. Need one of those items and there are issues that, even individually, seem to be well out of place in any dedicated player. And, in combination, render the player unusable for me for my use cases.
And, I think this experience confirms that until Android has native support for multiple output sampling rates, with an option to bypass any kind of resampling, it's not something I want anywhere near a dedicated audio player regardless of who makes it or what other issues may exist.
For me, just too many issues, with the distortion and Bluetooth range/dropout issues being complete deal killers (I could probably come to live with the funkiness and instability when using external DACs if those other issues were not apparent). So much promise, but it fails in actual execution.
[COLOR=FF0000]So ... I am returning my DPX1 today.[/COLOR]