iBook in two volumes

Apple have one book delivery process... you deliver A book - if you have a series planned or you decide your book needs to be in two parts - each becomes a separate book and you need to adjust your charges per book - which you decide.

if you split one book into two books.. each book must have its own cover ( confusing if you use the same design - but your choice) it must also have its own screen shots and everything in the deliver process.

The delivery process allows you to choose one price tier in your chosen currency - which is then used as the basis of all 51 stores currencies when converted - if you opted for all stores. Therefore with a large volume, split into two books - each must be priced as a single book.

If you want to charge more for Book 1 than Book two, in a way you are rewarding the buyer of both both books with a discounted price.

Not sure that two books dealing with different subjects can be termed a series...but... fact is no matter how want to kick it around... you can sell only one book at one price - not two books at one price. What price you put on each book is your choice, You have no way to track who bought book 1 or book 2.

Your own comments indicate the books by their content, will sell on that content to those who like it.

Fact is, at this time, you don't have other selling options from Apple.