From looking at my 8000A manual, I read it that you are going to have to do the internal modification whether you are going to use it as a preamp or power amp. You cannot simply hook up the A and use it as a preamp (if I am interpreting the manual correctly).
That being said, if your speakers have dual binding posts, I would strongly recommend a biamp configuration as I think you would derive the most benefit and best sound quality that way. I would definitely go for it, probably using the 8000S as the preamp unless you have an analogue source and want to use the MC/MM in the 8000A.
That being said, if your speakers have dual binding posts, I would strongly recommend a biamp configuration as I think you would derive the most benefit and best sound quality that way. I would definitely go for it, probably using the 8000S as the preamp unless you have an analogue source and want to use the MC/MM in the 8000A.