Why do you have two recievers? Why don't you just use the one with the amp. Does the old one have something special about it?
Anyway, to answer your question, your reciever(s) should have an auxilary input to them. Well, if they do, from your old one, get a 1/4 in. mic cord and strip one end. At that end you should see 4 wires(stereo), 2 gnd, and two output(r and l). They are going to be small, so you would probably want to solder bigger wires to them. When that is all said and done you need to plug the wires to there corresponding location on your old reciever(the speaker outputs).
Now you have the other end, you need to find the auxilary input on your newer reciever. Plug it in. And plug your speakers up, and turn on. It should fire away.
Now this is based on that you do have an auxilary input. But if you don't, maybe you have a phono input. If you have a tape input, do not use that one. For your sound wouldn't be amplified. I don't think.
If you don't have any, then i might have to think about it some more.
Hope I have been some help.