[Cromseth]

The skin meanwhile seems to download and use that art but I dont have "control" over that files (they are not obviously in movie folder).

Settings looks ok. I thin MQ uses ArtworkBeaf or ArtworkDownoader to get the additional images. Both addons shoud have an option like "use local images instead of downloading them". 

Ok. I will study if that is the cause. Its weird because I dont have any of that artwork addons installed, but maybe I can try installing and see what happens.

Just to be sure: if the sync was ok the "choose artwork" menu (as you posted) should index that extra artwork or is skin related? Can be that artwork "indexed" or "assigned" to the movie in that menu independently of its showed or not? Asking for trying to locate faster the problem.

Thanks!

EDIT: Any idea about the other issue in audio tracks? I did the ffmpeg "capture" you posted but the output mkv only use first audio and first subs tracks, not all of them.