Hi,
You may get better responses if you post in the Double Bass forums as you are asking about a DB here. I don't play a DB but I had a Kydd electric upright bass that used a Fishman BP-100 piezo pickup, so I had to consider the preamp issue.
In general, piezo pickups are high impedance devices. They need to feed into input impedances of 10 mg ohms or else they lose most of their low-end response from impedance mismatch. Few amps or mixers have special inputs for piezos, so it's best to put the signal through a preamp before it goes into the mixer, which will balance out the impedance mismatch. I used a Fishman Model B preamp.
Bob Gollihur, a talkbass regular, knows all about the K&K Bass Max pickup that you use.
Go to his site here:
http://www.gollihur.com/kkbass/bassmax.html
and click on "Not sure which Pickup or Preamp to Use" graphic on the right hand side to email him your query - he is THE man to ask about preamps with this pickup.
Hope this helps a bit.
