Regarding the I2S out/in - please have you considered a firmware option where one of the I2S lines could be I2S master input, for connection of an ADC. clocked to XMOS clock (i.e. running synchronously with the DAC), and adding USB endpoint IN to XMOS firmware to send the data back to the USB host (regular async input, without any feedback endpoint)? That way your very nice DAC could be complemented with a decent ADC. Since you already have all the hardware on board (bi-directional I2S ports, USB, XMOS), it would “only” require a change in XMOS firmware.
Thanks a lot for your reply.
Best regards,
Pavel.