Talk to me about USB Audio with Android Lollipop

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I have a Nexus 5 & have discovered that Lollipop(Android 5) natively supports audio over USB. Finally! I could have rooted my phone to get this with previous versions of Android, but chose not to. So, who here has gone this route?

I currently use PowerAmp as my player. Do I need a specific app to take advantage of this? Will I be able to use any USB DAC? Do I need am externally powered DAC or will the phone's USB be able to power it? Battery run time?

Respectable USB dacs in the $150 -$200 range? This would be for a desktop headphone set-up at my office. I have a Schitt Asgard2, so no amp is required. DAC only. I don't need the co-ax or optical, but the Schitt Modi2 Uber looks interesting. Though a number of you did not like the original Modi.

-Dave