Plexamp to USB Radio

I started using Plexamp on an Android phone and want to output the music via USB cable to a tather old radio (on a boat.) The radio supports USB MTP and MSC. It has no Bluetooth support. The radio by default finds music in the mainstorage/Samsung/Music folder using MTP and has the ability to select other folders.

My questions are:

  • Does Plexamp on Android generally support streaming via USB cable?
  • if so, which USB protocols are supported?
  • I did not find a way to configure streaming to USB either in Plexamp or in Android. How is it configured?

Unless it can be accomplished by Android natively, Plexamp has nothing specific for USB.