Clearing up some of the mis-information. We should all try to post responsibly to avoid ionic pantameter. A new installer could lose jobs in a tough economy by spending more of the customers money than need be.
1. My company is not permitted to use any fiber cement board in conjunction with any schluter membrane be it Kerdi or Ditra. They tend to absorb an excessive amount of moisture from the mortar, even when presoaking them, creating a weak bond. My recommendation is to use a true CBU using the manufactures fastening and setting guidlines.
2. Not specified anywhere to use double layer CBU's. 3/4" wood substrate sloped 2% away from structure. PREMIUM! unmodified mortar > 1/2" CBU bisecting cooresponding panels with each other as well as the joints in the substrate > Ditra > Kerdi Band > Tile.
3. Use Ditra XL for large format tile or natural stone for added load support and flexibility or over 24" on C joists.