How to assign effect to knobs on MainStage?

Hi,

I have mainstage and I am loving it, I also have a midi keyboard that plugs in and works just fine. When I assign the knobs and sync it with mainstage it's all good, I move the knob on the keyboard and it shows it moving in mainstage which is perfect. But what I'm having trouble with is this...

When I assign an effect to a knob, it doesnt work...well, let me explain.

If I assign modulation, or volume or pitch to a knob and if I play my keyboard and turn those knobs on my keyboard it works just fine. But if I change it to an ATTACK or DECAY or VIBRATO effect, there is no change... no matter how I twist and turn the knob. It's all hooked up fine, same knob that works for volume and pitch and all.

But basically what I really want to be able to do is hook up ATTACK and RESONANCE and other effects to knobs so I can change them while playing.

Does anyone know what I am talking about?

PLEASE, I will be very greatful if you help me out on this one. I have tried almost everything.

Thank you,

Conan