Stream Spotify through a USB connection to Yamaha CD-S300 using an Android device

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So, I'm using the USB connection on my Yamaha CD-S300 CDP to allow me to Spotify through my system. I currently have one of my iPads connected to the CDP

I'm very curious on how this is done. Does it "just work" with iXYZ devices? It doesn't work out-of-the box with the Android devices I tried. Is there a way to make it work? I've searched a lot and found many references to "USB audio" on Android, but none of these led me to any results.

I'm currently trying to retrofit an Android 4.1 device (HTC Desire X) and an Android 5.0 device (Samsung Galaxy S4) to be able to stream Spotify through CD-S300's DAC.

Thanks in advice! Any hints or advice is much appreciated