I’ve been using mine a lot for the last two days, and will again tomorrow, so can investigate properly then. But I hardly ever use the front panel, so what follows may be rubbish!
AFAIK all of the desk’s functions are accessible from the Pac’s front panel – you do not need an iPad/phone. But I don’t think the soft keys can be made into mix select buttons, those are on the touch screen. The 16 channel select keys along the bottom are a user layer, so you could put have the Mix Masters there, I think, if if that’s what you want to get to quickly. But I don’t think that’s what you want is it?
I’d not want to mix a show on the desk alone anyway, as getting from one control to another can be several button (real and/or virtual) presses away. The apps are much easier and faster to get around on. In fact I’m considering swapping my Pac for a SB. Having the soft keys work as mix select buttons would help I guess, but I’d still use my iPad!