Bryston 9B SST2----Stupid Question


I have a Bryston 9B SST2 5 channel amp that is part of an estate that I have agreed to sell for a relative. The owner of the unit is deceased so I cannot ask him this question. No manual.

I'm trying to test it to make sure everything works before I sell it. I've got the speakers hooked up. I've got the pre-amp hooked up.
I just can't tell how to hook pre-amp to the amp. Each of the five channels has two speaker out connects (L/R) but only one single ended or one balanced. How do I plug in the L and R RCA lines out from the pre-amp into the amp?
Sorry to be so stupid about this but I'm stumped.
n80