Hey Tom!
As for “What should the settings be in each zone”, the defaults are setting the max to zero and the minimum to -80. That isn’t a “should” though; what “should” be is whatever works for you and your setup. Looking at the max rating for your speakers would be a good start to avoid damaging them, then just trying what works best for you as a max volume setting.
Beyond testing different settings yourself, if this feels like a software issue we’ve got a good one-size-fits-all solution for those, if neither of those options fix it I’ll have to suggest you reach out to us at support@micro-nova.com and we’ll explore if this is a hardware issue