
Not sure why the switch is required. Maybe I am missing something?
Modern audio gear normally use impedance bridging. This means the output impedance of the preamp is 1/10 or less of the input impedance of the device it is plugged into. The idea is the load impedance is so high that it is viewed by the preamp as open circuit. With impedance loading, it should not be a problem to drive more than one device with no volume drop.
I don't see how the second diagram could possibly resolve the volume drop issue. If I understand what you have done, the only difference is the first diagram only switches the hot, which should not be necessary. The second diagram switches the hot and the ground. With the second output selected, both circuits are electrically the same. One output is driving two loads.
So I suspect the source of the volume drop has not been identified.
AFAIK both diagrams are functionally identical to this when the second output is turned on.
Unless you need the ability to toggle the second jack on and off for different parts of the show, I would eliminate the switch.