I also need a binding for a Kastle mx88 but I've never heard of anyone wanting to move that binding forward of the line so if you can recommend a good binding I would appreciate it.
My DIN is 8 and I am a extremely aggressive skier.
The Rebel ISpeeds you have will easily accept the Head/Tyrolia Freeflex 14 Binding. This binding puts you in the middle of the din range of 4-14. The factory installed/drilled plate allows you to move the bindings fore/aft in 1 cm increments. Many users like the bindings on that ski moved 1 cm forward of the factory line. The Kastles offer a re-badged Head Powerail PRD12/14 Binding as a factory option. I use both of these bindings and like having the extra safety of the diagonal heel release.