The MIDI Arranger versions (WK2-in-a-box) have the "Mixer Lock" function available in the General menu. However, the keyboard version did not offer this function. What I cannot be certain of is whether this function was added to the keyboard version in a later o.s release (since the module was designed some time after). Perhaps if you update the o.s you will find that this function is available. Maybe Paul D can find out for sure.