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.