#1) Are you sure that is what is happening? Some subwoofers become active when they detect the signal coming to them and often they are not sensitive enough at low volume to kick on the sub amp. Check to see if there is a switch on the back that lets you set it to "always on" or "auto on". If so, switch it to always on and see if that fixes it. If your receiver actually does that, I have to believe it is defective!
#2) No, it does not have the pre-amp outputs you need! The earlier R-S700 had this feature, but the integrated amps including the A-S700 from the same period did not! Go figure! Here is the R-S700 and the connectors you want are just left of the subwoofer connection: