You should be able to use any line-level input on the RA (do NOT use phono jacks) including the tape loop. Just plug the L/R RCA cables from the L/R line-level output of the RSX to the 'Tape In' jacks of the RA. Then select tape (or whatever input you use) as the input on the "Listening" knob on the front of the RA. If you are thinking that you will bypass the preamp section of the RA by using the tape loop versus another input, that is not the case. Only the 'Tape Out' jacks will be passed at a fixed volume level. All inputs, including tape in, will pass through the preamp section before going to the amplifier section of the RA since you have no 'pre-in' connection.
To avoid damaging your speakers from excessive volume, MAKE SURE AND TURN THE VOLUME ALL THE WAY DOWN ON THE RA until you are able to see how loud the output signal is from the RSX. Once the RSX is powered up, use its speaker level test tones and a Radioshack analog SPL meter to find the volume position on the RA that matches the SPL level of the other speakers at your listening position. Note that volume level and always use that setting when using the RSX as the signal source.
Some manufacturers specify the 'unity gain' position on the volume control so that, when set there, the volume pot is (almost) bypassed. If you can get that info from Rotel, then set the RA to that volume position and use the speaker level setting in the RSX to find the volume that matches the other speakers at your listening position. Again, keep the volume setting on the RSX down until you see what the volume is coming out the RA to avoid damaging your speakers.
Good luck.
To avoid damaging your speakers from excessive volume, MAKE SURE AND TURN THE VOLUME ALL THE WAY DOWN ON THE RA until you are able to see how loud the output signal is from the RSX. Once the RSX is powered up, use its speaker level test tones and a Radioshack analog SPL meter to find the volume position on the RA that matches the SPL level of the other speakers at your listening position. Note that volume level and always use that setting when using the RSX as the signal source.
Some manufacturers specify the 'unity gain' position on the volume control so that, when set there, the volume pot is (almost) bypassed. If you can get that info from Rotel, then set the RA to that volume position and use the speaker level setting in the RSX to find the volume that matches the other speakers at your listening position. Again, keep the volume setting on the RSX down until you see what the volume is coming out the RA to avoid damaging your speakers.
Good luck.