There is no way to probe a USB device and ask “do you support DoP?”, so we offer DoP as an option for any device that support 176.4/24bit output.
DoP (by design) sounds like a very quiet hiss when played back through a DAC that doesn’t support it–this prevents damage/loud sounds when things are misconfigured.
The Prime does not support DoP, so “Convert to PCM” is the right choice.