My thanks to all who responded!

The problem with the Pioneer DRM-610 turns out to be that it's old
enough (it's from 1990) to need the LUN present in the SCSI command
itself.  Thanks to Michael L. Hitch, who explained this to me, I've
now got a local hack in the SCSI driver so that it does this for me
for this particular drive.

I'll look into making a proper "quirk" for this, and send-pr it.

-tih
-- 
Tom Ivar Helbekkmo
tih@Hamartun.Priv.NO