Make sure you're dragging-and-dropping the SNES game onto "snezzi.exe" to create the "Game_Name.nds" file, which is the one you copy to your card. You need to find a way to load this .nds file to the 3in1 and launch it in DS mode, and I'm not entirely sure if the CycloDS menu can do this or if you'll have to use GBA ExpLoader. Perhaps if you rename it to end in .gba instead, it might be more manageable. Worst case, name it .gba, load it into the 3in1's NOR flash, then use the CycloDS as a passthrough device to boot it in DS mode.