Two preamps connected to one amp?

Is there any harm and/or sound degradation in connecting two preamps to my McIntosh MC252 by utilizing the Balanced and RCA inputs? There is no Bal/Unbal switch on amp. Of course, only 1 preamp will be powered on at a time. My main preamp is the McIntosh C42, connected by balanced cables. I also have a tube preamp that I would like to use for a separate CD player. I would connect that to the amp using the RCA inputs.
Thanks for any info.
You should not do it without an A/B switch. You will probably damage the preamp that is not powered on.
Any recommendations for a switch that has RCA and Balanced inputs and output of Balanced?
You could connect the CD player to the tube pre and go out of the tube pres tape out into the Mac therefore bypassing the volume control of the tube preamp. I don't know of an a/b switch that has balanced and RCA ins and outs but I'm sure one is available or could be built.