A few minutes of searching suggests that DiskCopy 6.x format is NDIF, which I think is just a raw disk image in the data fork with all the metadata in the resource fork. If you copy the file to a Windows volume, it'll split the forks and put each fork into a separate file. If the data fork file is exactly 1,474,560 bytes (512 bytes times 2880 sectors), then it's a raw HD disk image and should work fine with Floppy Emu. Latest firmware no longer cares if the file extension is .dsk as long as the image is the right size or has the right signature.