Well, I also am fine with large books. Don't know about the print on demand being a problem as I ordered my Earthdawn books from one, and they are huge. (And just fine as far as books go.) I get books (snail)mailed to me all the time, no problem.
Perhaps, the specific map booklets can be different files, but part of the same purchase. So, you order it all as one product, but the printing is in 2 books, maybe with a cool folder. (I like cool folders with neat art and stuff on them. Not sure what problems that may fix or cause, as I am not in the printing/publishing business.