[Be]

So long as the external DAC is a self-powered USB host, I think it's possible. Those seem like some fairly hefty caveats to me, although I admit I don't have a great knowledge of the kinds of interfaces that are common for external DACs.

There's a trick to supply power to any USB device even if it doesn't have its own dedicated power supply: a USB hub! Nowadays some USB-C hubs have a port for USB-PD input that can both charge the host and power the peripherals. I use a little USB-C hub with a battery pack to power my RME Babyface Pro to use it with my Android phone (most Android phones with USB-C ports can supply enough bus power but the Babyface Pro drains their battery in like an hour). It would be cool to be able to do this with Tangara!