Hello Captain Reg
I have Turnigy TGY i6, it is the same as FlySky and Rx will work on both. I use two boats all the time, with a Glyn Guest V&W and a I class and two Springers and two more tugs. You have six channels, i use one stick per boat meaning up and down, forwards and backwards and left and right.Bind boat A on the left stick, then bind boat B to the right. It will work, what does not work is three. On the Turmgy Tx you have two rotary controls and more switches. I thought two sticks two boats fine two channels to go then, a Liberty ship a destroyer or two or a fleet tug. No three wont work, it wont work on Spectrum DX6 ether. One thing is you will need a spring return up and down on both sticks, because it gets interesting. Its your very own steering competition very much so with two Destroyers that look similar fifty feet away.
Good luck...