Ok. So what the OP has is actually a raspberry PI3 with a dac connected to the GPIO pins. A The raspberry PI3 has 4 usb 2.0 ports. The OP can connect the thyaga dac to the USB port and get the sound. Since this is a RPI3, it will be running linux and most probably it will be running mpd.The OP wants USB output. The Swara is a nice DAC and streamer but it has only analog output.
If it is running mpd, then any mpd client (like mpdroid on android) will work and will show the thyaga dac connected to the usb port and he should be able to chose the output (whether it goes to the current RCA out or to thyaga dac). Worst case if the existing device is not running mpd, he might have to connect a monitor once to the HDMI port and login to the streamer and configure it.
@aurobindosaha If you speak to Shiva, I'm sure he will guide you how to connect the thyaga DAC to the existing USB port on the streamer.
EDIT: If you are interested, I too can guide you. I'm very familiar with these SBCs (Single Board computers) and all my bedrooms have these to play music. It is really not rocket science to connect any usb dac to the device.
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