Change in Amstrad GX4000 emulator settings in order to play games
MAME/MESS cores do not run Amstrad GX4000. It needs to be changed to lr-caprice32 core (ok we can edit the emulator settings for now). But in order to run the games you have to set also the Model to 6128+ in the core options first in Retroarch. The question is how to do that inside DIG.
Ok I found it. I put some lines in retroarch-core-options.cfg in DIG and games play now !