2 systems one set of speakers?????

Hello All I have a question that maybe someone out there can help me with. I have a pre-amp, amp, cd player set up by its self. and I also have a receiver and another cd player that sound really good together for rock cds and the cds that don't sound as well on the pre-amp set up. Is there away I can use the 2 systems through one set of speakers?? So I can play the pre-amp set up and then switch to the receiver set up on the same speakers. Can I run 2 sets of speaker wires to the same set of speakers?? or will this damage one or the other. is there anyway or some thing I can do? I'm new at this so please someone help THnaks