Cheapaudioman is now reviewing an analog preamp , the schiiit Cara together with WiiM ultra . His opinion is that the preamp make the Ultra sound even better than having the Ultra connected directly to the poweramps.
What he has done is lowering the SINAD with the Cara preamp and a set of cables extra , possible with a slightly higher output impedance from the Cara driving the power amps.
The ultra internal dac uses Opa 1611 at the output and has a very low 11 ohms output impedance so - theroretically optimal to drive power amps directly with highest possible SINAD .
So, what sounds good for the ear is not certain and has nothing to do with high SINAD