Custom cc set and transpose

[Biskop Brask]

Hi!
I use a studiologic organ plus keyboard. In custom cc set you can select transposition, but the value 0 - 127 only gives transpose 0 to +7. How can I transpose 0 to -6? I wish value 0 - 127 would cover -6 to +7. Perhaps i am doing something wrong (besides learning everything in all keys).
Cheers!