you can look for a female 3.5mm with an rca in the other end of the cable or an adapter and plug it to the sub out of the receiver. It is ok as long as you enjoy what you hear.
I also started with a cassette recorder, tv audio in as center and a computer audio monitor plug into a dvd player audio output. It serves me well as far as audio is concerned but connecting them all is like all my life ika nga. your a great deal better cause you have a receiver and a sub woofer. so go, go, go.