Hi Barbara...
Just throwing my hat into the ring.
Why not hire some active mic splitters for the day..(BSS are particularly good in the UK).
Input all the sources to the splits, One output to the Front of House desk, and the other (totally isolated) to a multitrack recorder..Tascam DA 88 perhaps?...I'm sure this sort of kit is available in the US.
You then have the luxury of remixing at your leisure.
Costs?
One days hire of the split racks...(They normally come in units of 4, so 3 racks should do...In the UK, probably about £30 a day.
Digi 8 track....Mmmm don't know, but 1 Day for the gig, and another for the Remix.

You'd need a body to make sure that the levels going to tape were OK, but it's entirely possible, and the results can be magnificent.

One thing to remember. Put out 2 Mics (One either side of stage) pointing at the audience.(Obviously FOH wouldn't use these!) Just to make sure that you capture the thunderous applause!!

I must agree with some of the comments above. If you want a decent recording, On no account take anything from the PA desk. You'll be so disapointed. Been there Done that!!
Good Luck with the project.Would love to hear the results

Best Wishes Ralphie...