Are you using the same set of speakers? I would worry about the other end. If you are connecting two sets of amp outputs to the same set of speaker terminals, that strikes me as a bad idea, because the amp that is on will be putting power into the output of the amp that is off. Seems like the potential for distortion at a minimum, and, at worst, the kind of thing that might blow up an amp...
Using Y-adapter to duplicate preamplifier outputs
Is there any loss from using y-adapters to duplicate an output on an amplifier? Case in point; I want to duplicate my preamp output to feed a ss amplifier and a tube amplifier. Both will not be used simultaneously. I just don't want the hassle of having to remove interconnects each time I am going to use one amp or the other.