Whether built-in or external, some USB DACs support 24-bit 96kHz or even 24-bit 192kHz sample rates. In Linux you can set this correctly with some PulseAudio configuration — I wrote about it before: PulseAudio sound quality tweaks on Linux Known facts: The Sony PHA-2 and ASUS Xonar U7 support up to 24-bit 192kHz over USB. The FiiO E17 only goes up to 24-bit 96kHz over USB. So the question: how do you configure PulseAudio so it adapts to both devices at once?