You can use either method as you described. The (Y) cord method is simple and obvious that will require no programing effort. That radio will support dual aileron servos though on separate channels. This has the advantage of allowing easier electronic adjustment of the aileron surfaces independantly and allows the ailerons to also be used as flaps or spoilers while still functioning as ailerons. I don,t normally reccomend using flaps or spoilers on a beginners basis as that comes with another set of problems.

You are correct with that Tx to use two aileron servos on separate channels you plug one to channel five. As to which you are going to have to refer to your manual. Basically you want to enable flaperons and this is what you would look for in the book.

John