Originally Posted by cat6man
until native usb audio support shows up in whatever follows kitkat, many folks use UAPP with an OTG cable.........no rooting needed.
For the Nexus 5 or any Android device there is both a hardware consideration, and also a software (music player app) compatibility concern. They are two seperate issues, added to those are the DAC's power requirement and whether the device can power it from it's own battery or not.
For the software or player app, thats the easier one, as another post stated the UAPP app will allow for hi-rez file playback on most Android devices whose stock/included music player app is incompatible. The developer doesn't promise it will work with all Android devices however, and I think they offer a trial version to avoid disappointment.
The hardware/device firmware issue is the one governing whether or not USB Audio is supported. The device has to support USB Host mode in order for the OTG cable connection to a DAC (or any other supported USB device such as a thumb drive) to work. I believe the OP's Nexus 5 does support USB Host mode, but I'm not certain.
The DAC also needs to support this mode of USB operation, and I'm relatively sure the GO does. But the issue of power requirement and/or the need for a split USB cable and external battery for powering the DAC remains.
I've only tried this set-up with the LG G2 smart phone, and everything was supported natively with it. The stock/included music player app supports up to 24/192 natively, and the OTG function worked flawlessly in connecting to a thumb drive to import .flac files, and then connecting to a Resonessence Labs Herus DAC for hi-rez playback.
I am not a huge Android fan, this was a friend's phone, but I had to admit the entire process was smooth and very fast, the sound quality outstanding. I was even impressed with the G2's sound quality through it's own headphone jack and onboard Wolfson DAC, the best I've heard from a smart phone.