You can only safely split outputs not inputs. You should get an outboard switcher.
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Don't do either thing you're talking about, both bad ideas. Just manually swap the wires at your preamp's XLR input when you want to change to the other source (with the volume off of course) -- probably what you've been doing. A little inconvenient, but works with no technical problems or sonic degradation.
Option 1) You won't hurt anything but each source will see as its load the output impedance of the of the other source in parallel with the input impedance of the preamp. Since the sources will generally have a low output impedance this usually results in low volume. In addition nonlinearities in the powered off source may introduce additional distortion. Not recommended.
Option 2) Once again, each amp sees the speaker impedance paralled with the output stage of the powered off amp. Typically this is a very low impedance. This could result in damage to either or both amps. Don't try it.