This is a common problem not only dealing with maple but other hard woods as well. There are several things I have done to help correct this. I have tried using capacitors connected to the hot side of the pickup, and grounding the other side. Use a .0022 mfd capacitor or .0047 mfd capacitor. Using the small capacitor will permanently roll off the high end unless it is removed. Another thing I have done is to use a weaker magnet. I've calibrated magnets using my "Dun-ager" which is an instrument I built to control the strength of the magnetic field. Having a weaker magnet also rolls the high end off. As you decrease the magnetic field you will also notice a drop in output from the pickup. If your pickup uses a Ceramic or Alnico 5 magnet try replacing it with an Alnico 2. Another permanent way to decrease the brightness in your guitar is to try using lower value volume potentiometer. If your instrument uses a 500k pot, try using a 250k pot. If you use a 250k pot, try using a 100k pot. Use audio taper potentiometers for the proper volume increase. You can put in a hotter pickup that has a higher D.C resistance. If your pickup has a D.C. resistance of 7.8k, try putting one in that might be 8.5k or higher. Usually when you increase the D.C. resistance you get more output from the guitar. But not in all cases. If you have a custom pickup built using a thinner gauge of magnet wire (say 43 AWG) and the same number of turns as the heavier (say 42 AWG) they will have about the same output but the 43 AWG will sound warmer. There are many variables so find an experienced repairman to help you.