Unless your receiver has 2 tape monitor loops OR you have OR buy a Radio Shack tape control center, you are out of luck. There is nothing wrong with cassette tapes. With quality tapes and deck they will sound great. That's all you need most of the time. And they are reliable as well.
some receivers have both a tape and an aux input. if so just use the aux for your other deck.
If you only want to connect the second deck for listening (not to record), you can connect the cables to a different pair of input jacks (e.g., aux, tuner, video, cd) on the receiver. DO NOT USE the phono jacks.
If you are looking to record to both decks, your receiver or preamp must feature two tape loops (tape in/tape out). In other words, there will be two tape outs on the rear of the receiver or preamp.