The problems I have had from my galvanically isolated XMOS Off-Ramp 6 USB interface are finally being resolved. They were on-die timing issues as I suspected, from the third-party design I contracted. I am now getting reliable 176 and 192 PCM playback over I2S (SE and HDMI).
This means that it could be installed in the Overdrive SX DAC in place of the older USB interface and the Ethernet interface.
The S/PDIF and AES/EBU outputs are not working yet, but I'm still debugging. I fully expect this to beat the Berkeley XMOS interface.
Have not tried DSD64 or DSD128. Should be able to get DoP DSD64 from the S/PDIF when it works, and native DSD64 and DSD128 from the I2S, maybe even now.