OK, well if was me in that same situation I first would not wait for mackie to solve the problem by gig time.
Plan B needs to be in place. Like I said earlier see if you can borrow a few iPads, you don't need to borrow another mixer or find anyone with a 1608, all you need is their basic iPad, it will take 5 minutes to load the app on them, after the gig delete the app and return to the owner.no harm done, and the gig goes on.
Now, let's say no one I know has or will load me an iPad, I now have option C, just like back in the Stone Age we do a sound check for monitors and FOH and let the sound guy run mains and monitors with your iPod that you
must have to go with the 1608. After he/she gets a decent front mix, they come up to the stage and watch while each person signals what changes are needed in their monitor. If there is NO soundpeprson.....get one!
Just kidding, if there is no one running sound for you and you're doing it yourself from the stage, let the individual
Band members tell you what they need between songs and make minor adjustments one at a time.
Yes, it's primitve, it's how we did it before there was iPads,iPhones,iPods,Ijails. Just put up with it to get thru the gig cause the show must go on. It won't be forever and the app will be ready before you know it.
Using a spare analog mixer won't be any better.