Doing a few experiments, to see if the M3s will work as a USB DAC with my older Google Nexus 5 phone (rooted & running CyanogenMod 13.0 / Android 6.0.1).
The result were both interesting and ironic.
I have a couple of different OTG "Y" cables, that can charge the phone & DAC, while flowing data between the two.
The first one has a MicroUSB female power input jack, which allows the regular charging cable for the phone to be used -
https://www.ebay.com/itm/Charging-D...B-Male-OTG-Micro-USB-Female-Y-US/362116512016
The second one has a right-angle MicroUSB male plug for the phone, but a regular USB-A male plug for power, so a USB extension cable has to be used -
https://smile.amazon.com/gp/product/B00V81L9M8/
(
NOTE for Second Cable: Even though the info on Amazon says it doesn't charge the phone, I can assure you that my phone is staying at 100% charged, while connected to the cable.)
For both cables, I'm using a generic 3-ft (or 1-meter) USB-A male to USB-C male cable, that connects between the OTG cable and the M3s.
The ironic thing, is that USB Audio Player Pro glitches badly while streaming radio stations from the Internet (I don't have music on my phone, since the memory is full of apps & photos). I've tried various combinations of settings, to try and eliminate the glitches, but haven't been successful, yet.
Pandora, TuneIn Pro, and Spotify all sound great, when the M3s is connected as a USB DAC, but they require that UAPP be set as the default USB DAC app (if the defaults are cleared in the UAPP app settings, no audio is sent by the other apps...
)
The M3s ($280) has a similar architecture to my Onkyo DP-X1 DAP ($600) - Dual DACs, Dual Amps, Balanced Output (130mW / M3s; 150mW / DP-X1).
The M3s can operate as a USB DAC, but doesn't have WiFi.
The DP-X1 has WiFi, but it can not operate as a USB DAC.
When I'm in a location that has WiFi, then my Onkyo DP-X1 DAP can stream music from any of the apps that will run on my phone.
But, if I'm in an area where WiFi isn't available, I can either use my phone (or tablet) as a Hotspot for the DP-X1, or connect the M3s as a USB DAC.