I don't know if I'm getting your answer. You say "why not" when I state that I never copy from DVD to DVD and then admit that you copy everything to the HD first yourself. I am always starting with a DVD9, therefore I will never go 'drive to drive' because I will always need temp files written to the HD during the process. BTW - I believe it is the second button - "clone DVD" - that performs a DVD5 to DVD5 copy. (If you happen to be starting with DVD5 that is!) Therefore, I would think that the best setup for this type of operation would be:
DVD-ROM - ss
Does this make sense? The DVD-ROM to HD rip will benefit from being on separate channels, and the HD to DVD-R/RW will also benefit from being on separate channels. I could certainly be wrong, this just seems to make the most sense to me.