[Kong]

I assume you are referring to Score Mode.

Sorry not possible. Fast forward just plays as fast as your computer can go. If you can manage to slow your processor down through some other means then you could slow down the fast forward. I will try to add this feature in the future.

For muting the only options are
1. Press ` then hold left until the green bar goes to zero. Then press ` again to get rid of the volume bar. ` is the key in the top left of keyboard left of the 1 and below the escape key.

or 2. You can press Tab. Select Slider Controls. Hold Left to slide Master Volume all the way to the left.