It's probably not a bad idea to contact them for suggestions or ideas if you need them. I guess it will also depend on how you want to wire in the Piezo with your existing electronics. I have a custom shop Corvette that haas a piezo in it, and in order to get the electronics for the piezo in the cavity along with the MEC 3-band electronics they created a separate cavity for the battery. The circuit board takes up a good chunk of the room in the cavity and is stacked on top of the smaller MEC circuit board. It's got variable resistors to adjust the volume for each individual string plus two others, one for overall volume and the other I'm not sure what it does yet. If your battery is already in a separate cavity, then you shouldn't have too much trouble with fitting it all in there.
They also replaced the third knob with a stacked knob and that controls two of the 3 bands for the EQ, and the fourth knob is a stacked knob to control volume and tone for the piezo. The output from both go to the same jack. You can also wire it up so that you have separate outputs as well (Check out the BIGBASS Streamer Fretless Extreme in the custom shop for a great looking bass with dual outputs... It's pretty sweet!).