Just because some routing is defaulted on the x32 doesn't mean that the engineer hasn't loaded his showfile and changed all the routing.
stay away from the monitor outs, that's the solo/pfl bus and will cause you problems when the engineer solos a channel in his headphones
By default, there is nothing assigned to the AES out, you have to get the engineer to assign whatever bus you want to it.
I've spent most of 2015-2016 touring with an x32 and the only thing I use the onboard recorder for is a quick 2 track file so the band can listen on the bus after the show.
it's not terribly reliable, it hates certain brands of USB drives, and can insert diginoise and dropouts if you don't have it formatted correctly.
Multitrack via the FW/usb out + a normal AUD/SBD mix into my DR70D makes sure that every note is recorded throughout the whole tour.