Hello,
nice to hear another Catweasel and MMC user.
I bought the Catweasel PC on 2006 and it never made any working floppy for my Amigas. I always had "not reading disks" or "checksum error" when I writed the .adf to the floppy.
But it happens that now I am reading that with the newer version of the image tool the floppies works fine.
So when I have the time I would put the Catweisel again in my PC XP .
I never tried to write .D64 on 5,25 floppies and I am sorry to not be able to help you. Anyway consider to contact me for any RR Replay or MMC64 issues or program.
I own both the cardtriges.
I wanna try the SID chip too on my catweisel but don't know if VICE could make the SID of the CAT work.
Cheers and good luck with the .D64 !!!