Hi there Cabinboy, its possibly time to do what every modeller has to do
read the instructions once again 
not being cheeky mind, but, I know on one of my Futaba sets I had to read and re-read and re-read again the instructions - until the penny sank in for me.
As it turned out, what I was asking it to do, it wasnt made to do. :'(
As far as switches 5/6 are concerned, on your Futaba model. I will not stick my neck out and say they cannot be changed to a centre-off switch. Because, you can guarantee someone - somewhere will be able to do it. But, I will say, it is well out of the reach of the even above average person. To be honest with you, not only is it a hardwear change over job, but it may also be a softwear job as well - re-programming some chips inside.
However, the other thing that you really want to think about is, although the technology for the 2.4 isnt a new technology, your particular set is a new boy on the block. It hasnt ran any length of time, and you can guarantee all the teething problems havent been sorted out with it, as yet.
So, if you, or anyone else goes around opening it up and altering it, it will invalidate your warranty straight away. Say, for arguments sake, one day something goes wrong with the softwear in side, which would have been covered by the warranty, it will be no longer covered. Then, would it go in the bin?
The choice is yours, as they say.
If it were me, I would sit with servos plugged into the TR. instruction book out again, and sit and work it all out, until it does what you wish it to do. You know that the switching units are functioning correctly, you know the transmitter is functioning correctly. It may be you are asking it to do something it cant do.
aye
john e
bluebird