In MSX-DOS2, you can use FIXDISK to create an MSX (-DOS2) bootsector. Should be ok, although maybe a turboR can get confused and boot in DOS2 mode when you want DOS1. But ahwell... Depends if that's a concern.
John. I have the perfect solution. In a few weeks I am going to Rieks in Leiden and I happen to have a working nms8245 in a dusty dark corner of my MSX dungeon. If you like I can bring it for you, together with the proper (real) disks. You still have your moonsound do you?