Best Option - Connect the zone 2 preamp output to the input of the RTR. Set the zone two level and leave it alone. Select the source you want to record as the one for playback on zone 2. This option lets you listen to the tape you are making while it's being made by selecting the input you connected the RTR to for playback as your source for zone 1.
Other Option - Connect the front preamp output to the input of the RTR. This is a variable output so when you turn the receiver volume down the record level will go down too. Set the receiver to stereo or pure/direct mode when you want to record.