The Mesa Walkabout has a balanced DI, post EQ and FX loop. You'd normally use that plugged into the console directly with a balanced Xlr cable, as if it were a mic. There is no provision for pre-eq, however, so FOH will receive your EQ and FX loop sound.
The Fly Bass rig also has a DI out, equally post FX. There is no provision for having a Pre DI, so FOH will receive the FX.
If your sound fellow wants a 'dry' bass signal, it'll require the bass to be plugged into a DI box before the Fly Bass, with the Fly Bass chained from the DI box.
Hope this helps.