@sebdel - to use mra directly from mister we also need to mra software to read several zip files from zip property.
You can find one exame here:https://github.com/MiSTer-devel/Arcade- ... Amidar.mra
why could we have more than one zip?
because of different sets of mame (merged, nonmerged, slipt).
before crc functionality we had to provide path inside zip and with this we had several "rom 0" entries. Because now mister tries to match crc with all files inside zip, no need for path anymore. but different sets could have different file names and that's why we provide more than one zip.
if mister doesnt find the file in one zip, it tries to find it in the next zip and so on
(if its not exactly like this... is more or less)