Small update... Opened amp today. There are 8 jumpers marked with high/low, 4 visible on photo from "montr" thread and 4 more under small PCB on which switch 1-2 is.
Tried first 4 on low, sound degraded from what I can say, volume from mid and tweeter reduced and from woofers increased highly. No change on gong/pdc.
Tried another 4 on low, sound also degraded and I got big noise, even when I switched off radio noise was still coming from speakers.
I swapped all jumpers back where they were... In this way I get most acceptable sound but PDC volume reduced.
I think I will stay this way if my dealer suggest to recode back to Stereo as solution.
Will see when they call me.