You don't need any "package" deal in order to use the scenery in FSX and FS9, it's already sold as one.
As indicated on each product page:
http://www.fsdreamteam.com/products_kfll.htmlThe product is sold as 2 Products in One. This means, by buying one version, you will automatically get the other for free, since activation and serial codes are shared between FSX and FS9.
This means, if you have FS9 and FSX installed on the same PC and on the same Windows boot, if you install and register in either version of the sim, when you install the Trial in the other sim, it will already appear as fully registered without doing anything.
If, instead, you use FS9 and FSX on different PCs, or different Windows installations, you simply use the "Register Serial" function, to activate the other version on the other PC (or Windows install), using the Serial Number you'll find in your email receipt.