As you rightly state, the R102 is a receiver. It has a built in 50 watt amplifier and is not particularly designed to connect to another amp as a tuner would be.
You can probably connect the receiver to the pre-amp by connecting the tape output sockets on the receiver to an aux, tape in or tuner input socket on the pre-amp.
I would worry a little about running a receiver in that way as there would be no load on the amplifier. I would suggest you seek advice from SAE (if still extant) or someone who specialises in esoteric hifi.