Let's suppose the HRT microStreamer is compatible with the native USB audio of your HTC One M7.
music file >> stock music player (or YouTube) running on HTC One M7 >> USB OTG adapter cable + regular USB cable provided by HRT >> HRT microStreamer USB DAC/amp >> headphones
Each component should be separately tested.
Go to next test only if the ongoing test is successful.
. Test the HRT microStreamer with a PC or a Mac:
PC >> regular USB cable >> HRT microStreamer >> headphones
. Test the HTC One M7 with a USB OTG adapter cable and a simpler USB peripheral like a USB mouse or a USB keyboard:
HTC One M7 >> USB OTG adapter cable >> USB mouse
. Test the complete setup:
music file >> stock music player (or YouTube) running on HTC One M7 >> USB OTG adapter + regular USB cable >>HRT microStreamer USB DAC/amp >> headphones
If the last test is not successful, the current native USB audio of the HTC One M7 is apparently not compatible with the HRT microStreamer.
Then test the HRT microStreamer with one of the following three music player apps which include its own USB audio user-space driver (i.e. USB DAC driver):
. USB Audio Player PRO (UAPP): "Important: connect your device BEFORE starting the app, otherwise it will not get detected!"
https://play.google.com/store/apps/details?id=com.extreamsd.usbaudioplayerpro
. HibyMusic: free
https://play.google.com/store/apps/details?id=com.hiby.music
. Onkyo HF Player
https://play.google.com/store/apps/details?id=com.onkyo.jp.musicplayer
https://play.google.com/store/apps/details?id=com.onkyo.jp.hfplayer_unlocker
The Android media player framework can only output 48kHz PCM audio to an external USB DAC for the time being.
USB Audio Player PRO, HibyMusic and Onkyo HF Player can play and output high resolution audio. They can also play DSD music file and output DSD over PCM (DoP).
http://www.head-fi.org/t/595071/android-phones-and-usb-dacs/6285#post_11306308
A list of USB OTG cables:
http://goo.gl/4JyOe5
Android USB Audio is in the first step of development.
The FiiO E17 USB DAC/amp for example was not compatible with the first version of USB audio of the Samsung Galaxy S3. The E17 can now work with the S3.
It is not easy for the latest entrants (Samsung, Sony, HTC, LG, ..., 3rd party USB audio developers like UAPP developer or Onkyo, and now Google with Android 5.0 Lollipop) 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 should not ignore Android, the biggest computing device market share.
The XMOS Multi-Function Audio Design Reference is used by many USB DAC makers to speed up the development of their USB DAC compatible with PC, Mac and Android; and the XMOS developers test it against PC, Mac and some key Android devices.