I've only got an older version but it should be simmilar.
Don't use the wizard.. on the left menu select the CD on the dropdown,
and select the CDROM-ISO from the left list. On the right side you'll
see an option for start multisesstion or continue multisession.
For the 1st time on that cdr select the start multisession.
Then click on new.
Here on just like you normally do, add the files..
Now.. just name them differently(you could also add _s or _u for scambled/un),
also if you use the same name on a session in the future.. it will well.. block out the previous one with the same name.
Once you're done click the burn icon..
here make sure the "Finalize" is NOT checked.. and then burn away..
next time you want to add files, just use the continue option at the start..
That'll save you at plenty of coasters.
Bookmarks