Ok, I now have Sega Model 2 set up and working however I have a different problem than you do.
Firstly, I set up an exit key which was E, I also changed that to backspace (just to try trouble shooting)
However, I still get audio after exiting, but no visuals it just goes to a black screen.
I am using Windows 10 and the proper emulator for that system, I think I posted the link in this section.
However, I just tried MAME and I exited out of that system and went back and had audio and visual.
Which by my powers of deduction it is something to do with the emulator used and not AM.
If I ALT & TAB to switch windows, I can see the visuals running but when I go back to the system it just goes black.
Just to add I enabled the ResFix set it to Sega Model 2 (Arcade) which I have called the emulator. I done a shut down and reopened, but that has not fixed the issue.
* Also I changed the settings in the emulator configurations settings to match your 1280 x 780
Well that is weird as hell. As I was typing that * I lowered my resolution to 1280 x 780. I still never had any audio loss, but what I typed earlier about it going to a black screen that never happened when I was at 1280 x 780 desktop resolution, it went right back to the visuals and audio. I am guessing that it does not like 4K resolution, I will try it at 1920 x 1080 and then edit this.
Ok I just done a test on 1920 x 1080 and when I press exit it shows the video and audio works as well. However, when I set it at 3840 x 2160 it is just a black screen.
So it is 50/50 on who is to blame now. However, my audio was still working as I say so it is something to do with your mini PC and not AM or the emulator.
Regards
Mark