I always try to keep all my levels in unity gain as possible.I start from the first one effect in the chain,then second,then third etc as i work with my chain and i keep always the total and global levels to 100 90% off the time.The reason is,maybe in the middle off a gig,my b3 fails or crash.Then if i remove the b3 of my signal chain,my volumes stays right with the others devices around me,like other pedals,DIs amps,PA speakers and consoles.I try to emulate a real one pedalboard.
Mind you that the levels in the effect level is not always unity at 100,and in case of amps or dirts there is a difference in volume and loudness.
The only solution for multis of any kind is to hook them in inputs that is made for them,not MIC ones.Always Line ins,whatever form they have,XLRs or TRS.
Zoom XLR output have 100Ω or 200Ω output impendance cable depended.
Cheers