I am not familiar with the Lex, but I am with the Gallo.
I just had a look at the Lex users manual. I think that none of the main audio outputs will work. Except for the "AUX" all are filtered. Those except the subwoofer filter out the lows while the subwoofer out has a low-pass filter. Problem is the Gallo has its own log-pass filter, so you end up using 2 low-pass filters which does not appear to be a good idea. The Lex's low-pass filters will preempt the Gallo's low-pass filter controls.
With respect to the "Aux", I am not sure what "reserved for future expansion" means.
The audio out of Zone 2 seem not to be filtered. If you can get Zone 2 to see the same source as the "Main Audio Outputs", these should work. Use the "var" outputs there.
Hope this helps.