UPDATE:
Regarding the problems with MAIN volume knob not completely attenuating the signal and the signal being out of balance at low volumes...
...maybe we are too quick to blame the manufacturer while in fact the problem is us.
The Monicon XL comes with output trims at full volume. But once I've trimmed the outputs so that the regular listening volume is somewhere around the 12 o'clock position rather than around 9 o'clock position, both above mentioned problems become pretty much irrelevant / non-existent.
So the problems related to the volume knob are pretty much consequence of our ignorance of the nature of the analogue components rather then the design of the device.
So the solution once more, is to feed Monicon as strong signal as possible and attenuate the outputs as much as necessary for the main volume knob to be around noon position during the normal listening.
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Here is a video demonstration of my third and final problem and/or possible discrepancy between specification and function.