With DVD neXt COPY, I may be wrong, but I can't see any ability to split a DVD9 onto two SL backup media.

For those of you who remember the early days of backing up, the original (before Express or Platinum ) 321 Studios DVD-X-Copy (final version 1.5.2) did this beautifully. ...and even gave you a nice "Please Insert Disk 2" message at the end of Disk 1.

Whisperer