This approach will give you the piece of mind on using one system only but will net you the smallest warranty in the industry to my knowledge. 5 Years.
Remember the key step in my system is the sealing of the bottom flange to the backer boards waterproofing.
You might look into Wedi's system. I have yet to try them but they make a backer board similar to Kerdi Board and also have a sealant similar to Kerdi Fix. I'm not sure if the Wedi Board bows or flexes as much as Kerdi Board.
The biggest single problem with Kerdi Board is doing a repair later if need be or durning the installation. You can't bang the tiles off the wall with a hammer without risk of damaging the board below the tile not in question.....
If you want Kerdi Board - make it yourself with cement board and then Kerdi.
Now if you want to double the five year warranty when using Kerdi to a ten hyear warranty AND use modified thinsets* (much much better) then use Ardex Setting Materials X5 or X77 I believe with KErdi. Ardex makes a product called 8+9 which we recently embraced and are using on three projects as we speak. Ardex makes a product called SK Mesh which is similar to Kerdi Band. I would imagine it could be set to the tub's flange with 8+9
* Call Ardex to get the product details on the ten year Kerdi Warranty. You need to use the right products and grout from Ardex as well.