I recently purchased the Astell&Kern PEE51 DAC, because it supports Roon Tested, I bought it for testing. ROCK is running on a NUC 7I7BNH.
Because the PEE51 only has a typeC interface, it uses the NUC Thunderbolt interface to connect. Roon successfully recognizes the PEE51, but the album cannot be played, and there is no sound.
To the best of my knowledge, ROCK only supports audio output over USB. You would need to use a USB-A male to USB-C female adapter from the NUC’s USB port to connect your A&K PEE51.