Bingo... There's a very likely explanation for your trouble.
Betcha your drives and controllers are just fine. You problem is the
disks. Disk II's are known for not putting out enough electromagnetic
"oomph" to properly write on DD disks, which didn't exist back when
those drives were designed, and require more power being applied to them
to write a bit than the same bit that's destined for a single-density
disk - The end result is like trying to write on a tyvek disk envelpe
with a pencil - it "just doesn't take".