The TABLET, or the PHONE, is NOT just a Music Player. You can play Movies, Youtube Video's, Netflix, Play Video Games and much More. You obviously don't understand what I am saying. UAPP is ONLY a Music Player, That is its Primary Function and it is its Primary Failure. I don't use this, and millions of others around the world also do not only use these devices to JUST listen to music.
I am pretty sure everyone will agree that the tablet, or the phone, is not just a music player.
An Android phone is a general purpose computer on which existing/future audiophile music player application software, or existing/upcoming virtual reality audio-video player application software, or other existing/future application software can run.
http://www.head-fi.org/t/595071/android-phones-and-usb-dacs/6015#post_11185404
There are music player applications, video player applications, etc… using the Android system running on Android-powered tablet/smartphone.
Like every other music player application software (Poweramp, Neutron, Spotify, Tidal, etc.), UAPP is only developed for playing music. For other stuff (video, gaming, etc.), there are other types of application software.
The successful UAPP is certainly not a failure: it is one of the top-selling Android music players, and audiophile USB DAC manufacturers like Chord recommend the use of UAPP.
People on Head-Fi are mostly interested only in music playback, I tried without success to promote VR video player application software.
http://www.head-fi.org/t/595071/android-phones-and-usb-dacs/6255#post_11286714
http://www.head-fi.org/t/750519/the-headphones-for-movies-thread/15#post_11219841
However, I understand what you want (i.e. fully functional native USB audio system software), but it is not fair to attack UAPP (i.e. just a music player application software among others) for what you want: system software and application software are two different types of software.
Native USB audio system software is overlooked by Android device manufacturers because the vast majority of Android device owners do not have / need a USB DAC to listen music, watch video/movies, play games, etc.
Android before 5, had no issues controlling all USB DAC's, Well not all but Most. Tablets like the Nexus 7 have been used over and over and over for in car installations. Lots of people who don't have Smart TV's or what not, use their Devices to connect to their TV's to watch Netflix, Hulu, Etc. We've been using USB DAC's this way, Much longer than UAPP has been around. We were not restricted to only listening to music. Now we are, unless we decide to use a cheap 5 dollar Analog Out Unit. But I'm not the only one that has Digital Out DAC's we've used for Surround Sound, SPDIF DSP Output, etc.
I have been involved in Android USB audio since the very beginning. I started the following petition:
https://code.google.com/p/android/issues/detail?id=24614&sort=-stars&colspec=ID%20Type%20Status%20Owner%20Summary%20Stars
And contrary to you, I do not have such a positive assessment on native USB audio before Android 5.0 (and also after Android 5.0):
. native USB audio is not functional on every Android device
. native USB audio is developed by different Android device makers in their own corner: different USB DAC compatibilities
. worse still, Samsung has different native USB audio (i.e. contrary to its immediate predecessor, a latest Samsung phone can be no more compatible with a given USB DAC!)
. lists of compatible USB DACs had to be created
. this long thread contain a lot of compatibility information and complaints.
So what are we supposed to do? You say UAPP shouldn't have anymore functions, because you don't expect more from a Music Player? I don't expect a Music Player at all. I expect a fix for ALL AUDIO. UAPP Instead of being a strict music player, could have been a driver, much like what people put in Kernels to control certain devices like the Wolfson DAC in Exynos Devices to enhance the high end built in audio, or other things like Chainfire does to enable USB OTG on Nexus 7 Devices. That way the Tablet or Phone, is not restrictive to JUST A MUSIC PLAYER...
I hope that was a little more clear.
There was an unsuccessful attempt to provide a third-party USB audio service system software by eXtream Software Development (i.e. UAPP software house) when eXtream was not interested to enter in the music player business (i.e. before the existence of UAPP).
And once the development of this USB audio service done, top-10 media player software development houses had been unsuccessfully contacted.
http://www.head-fi.org/t/595071/android-phones-and-usb-dacs/5565#post_10985943
Apparently, third-party API and third-party system software are not welcome.
We have to wait for a mature Google USB audio, when it will be compatible with a lot of existing USB DACs.
Apparently, since Android 5.0, more mature non-Google native USB audio is "replaced" by Google USB audio: hence they are a lot of compatibility problems.
It is not easy for Google, the latest entrant in the existing USB DAC jungle because the USB specification allows some variability.
http://www.head-fi.org/t/595071/android-phones-and-usb-dacs/4080#post_10270550
The latest entrants have to adapt their USB audio implementation to (most) existing USB DACs.
They have to be compatible with different interpretations of the USB specification.
Once the native Google USB audio becomes mature, it will very likely become a reference USB audio implementation in the USB DAC industry used for testing by the developers of new USB DACs (i.e. these USB DAC developers will have to adopt the Google interpretation of the USB specification), because a "professional" USB DAC maker could not ignore Android, the biggest computing device market share.
I think Google could speed up the maturity of the Google USB audio by enhancing the current Android Media API in order to avoid the current Android media player framework, the root cause of all current troubles: this Android audio subsystem has to handle a lot of other features like mixer, video audio, Android Auto or Android Open Accessory 2.0 (the mature ALSA USB audio driver is coming from the Linux community).
http://www.head-fi.org/t/595071/android-phones-and-usb-dacs/6195#post_11261908