I’ve bee trying this audio-in thing for the first time, and yes, you are right about the audio quality.
You get a mono signal out of Retrologue, and it’s weaker. You can mimic a stereo signal out of the Retrologue by using the delay: short delay time (approx 40 ms), Feedback close to zero, Delay L/R to around 0,90
These settings are just an example and it want replace a true stereo signal.