1. get rid of that 1x6
2. put down 2 layers of T&G fir plywood, two 5/8" sheets would give you min specs, but two 3/4" would be better.
3. use SLC if necessary, although it shouldn't be.
4. put down a layer of ditra if the budget allows for it
5. set your tiles
You should spend a week perusing johnbridge.com before attempting this project at all or asking follow up questions.