My new system is. …. WiiM ultra to SMSL PO100pro. to SMSL - SUI. to Q Acoustics SM20 powered speakers. While the straight through Optical route works well ( WiiM Ultra to Q Acoustics ) The other route as described above with USB c to the 100pro and optical from the 100pro to the SU1 then RCA phono into the Q Acoustics M20 does want to work. I think zI have the right settings on this kit. The 100pro and the SU1 seem to be problematic. But having bought them I want to use them to boost the DAC on the WiiM Ultra. Any thoughts would be welcome.