Yes, the 3 point has to come off. The lower mounting pin goes back in with spacers provided with the backhoe to keep the pin from moving out and contacting a tire. The pivot for the MMM linkage must be off the pin or it interferes with the backhoe mounting. They provide a bugee cord to hold it away from the tire. I have taken mine off because the linkage doesn't fit.
I'm don't know anything about an optional MMM cylinder, but it might be something to check into. If you want to switch from 3 point to backhoe often it may be worth having. I have not yet used my 3 point. I have only used my MMM, and loader. In fact I don't own a single 3 point attachment yet. /forums/images/graemlins/tongue.gif