You need to make aux1 (flaps) the master and slave the gear channel to it in a mix, then you can have each servo running on a seperate channel. I am assuming that you are not running retracts, correct?
Here is a link to the owners manual if you don't have one. It will tell you how to do it if your not sure, see pages 68-75. Hope this helps.
http://www.spektrumrc.com/ProdInfo/F...anual_DX6i.pdf