Maybe it is just something dumb as increasing +X dB in GEQ or PEQ and the software does not calculate and compensate with -X dB in preamp, and clips and generates all nasty distortions. RME had this figured out for ages now.They can be compared. I'm sure somebody will measure the Wiim with PEQ enabled. I know @VintageFlanker has some RME kit so perhaps he can measure both. I have no idea what the test would consist of but presumably looking for distortion caused by implementing same PEQ in both devices.
I do know that enabling the GEQ on earlier versions of the wiim firmware ruined the measurement scores but believe that was fixed in software.