Query about pCP and USB Dac

Hello
I am running pCP 6 on a pI 1 feeding into a PCM 2704 Dac set up as USB audio and output front:CARD=DAC,DEV=0. That works fine but not when I change DAC to a ES9018K2M SA9023 USB DAC. then I get no sound. What am I doing wrong.
Thanks
diode84