Welcome to the forum!
If you are referring to the Onkyo HT-S9100 system, then I believe that the answer is yes. I don't own a pre-amp, but I think that they connect to an amplifier using analog audio connections. The HT-S9100 has 7.1 analog inputs under the "DVD" input, and that's what I think you'd use.
Just curious - why are you thinking about adding a pre-amp to that unit?