Two line sources into one amp



I have a Benchmark DAC 1 which sounds much better driving my power amp directly and bypassing my preamp. Problem is I use the Audible Illusions M3A preamp for my phono set up. Rather than having to switch the DAC1 an M3A interconnect cables to the power amp, can I run both to a RCA combiner jack at the power amp without suffering ill effects (only one source putting out a signal at a time)?

I don't want to fry anything, or possibly compromise the sonics of one source with another.

Thanks for your help.
raygun
Thanks again everyone.

Checkeed out my parts express catalog. Nothing seemed to fit the bill, but I did find this switch on the WEB:

http://www.ramelectronics.net/html/40-814.html

Any thoughts?
The RAM switch will work. Niles Audio makes a signal sensing aoutomatic switch as well as as a manual model.
I ended up with a picture of a vidio switchbox of questionable construction for hi-end audio. If that is what you are looking at, I would pry a bit deeper into its parts quality for acurate audio transfer (ie: type of hookup wire, wiper type and build, and contactor material...silver prefered).