I have an RK24 with MMM and BH (among other attachments).
First of all, the RK24 does not have a separate subframe for the backhoe. It attaches directly to the rear of the main tractor frame.
Second, the MMM has its own subframe and linkage that attaches under the rear axles to the 3 point hitch. When the 3ph raises the lower lift arms, they pull on the linkage that lifts the MMM. Because of this, the MMM can be installed, but not lifted if the BH is installed, because the 3ph lift links must be removed to install the BH. Also, I am not aware of any way to lock the MMM in the up position. However, even in the up position, the MMM does not provide very much ground clearance. You will want to remove it for doing any 3ph related work. I install my MMM, mow my lawn, then remove it again. It's not that difficult.
Hope this helps.