ORIGINAL: Gray Beard
You will find that out in the trim flights, no one can say how a plane is going to act. Each planes set up is a bit different from plane to plane. I also use an old JR match box for some set ups. You can adjust the servos through it. I also don't ever use extensions, I solder in any wire I require for added length. I have had and seen too many extensions get sluggish with corrosion unless they are pulled and cleaned once in a while. If you do use extensions then pay the extra money and buy the gold plated ones.
GB nailed it right here. Although the Op has the capability to plug all 4 servos into seperate channels and dial it in, using Match Boxes or Smart Fly Equalizers is a great option. One could easily set it up to hook up either top/bottom or right/left. The devices will allow you to reverse the servos seperatly if needed and you can adjust center, end points. This allows you to match things up and dial in some differential without a complex radio.
IMO there is just no way to get all this done with Y connectors. If you doubt that statement then make some measurments and get back to us. I bet they are off more then you realize.