How is your /usr/kernel/drv/mt.conf setup? I know we needed to apply a patch to 
modify the Sun 2.6 tapes command...patch 105867-01if I'm not mistaken.  If you 
don't have this, then you tend to receive an error with the add_drv command 
telling you the device did not attach.  We're using an stk9714 attached to a 
ultra 5 running 2.6