Do you have any original game cartridges then?
Yes, a Burnin' Rubber from GX4000 (without the OS)
You can use those too, just upload lowerrom and basic to M4.
Yeah seems to work, i also updated the card to latest beta, but i think that's not what fixed the problem.
So, if i understand the txt, i have to choose between a better compatibility (slot 7) and simultaneous access from SD and disc (slot 6) ?
I guess it's because none did a patched lower rom like on the 6128.
Well not a big deal as the Plus won't be my primary target for playing game except 6128+ exclusives (like Rick 128+), so i guess i'll stick on slot 6.
EDIT : Slot 7 still works badly with C4CPC.
More testing : I have lots of problem trying to use both at the same time. Even with the C4CPC configurated to automatically launch red label burnin rubber (so in theory same config that with my other cartridge), i have roling reset on slot 7, and problems like protext garbled text on slot 6.