Changing your string might be a good idea. Here are some EQ tips that you should know about basses.
As a recording engineer, I find basses to have great bottom between 40-80Hz, the growlyness I find it between 300-600Hz and the click and brightness I find it between 1.5-3.5KHz. Of course this can all vary considering that some amps don't give you control over what frequencies you are boosting and attenuating.
My suggestion is:
1. Reset your EQ on both bass and amp.
2. Go to your amp EQ and turn down the mid frequencies, and start bringing them until you feel comfortable with how they sound, if after this you still feel there is too much low end or too much high end, try attetuating either one of the frequency ranges.
3. The rest is stuff that you can fine tune from your bass. And try changing the position of the switch for the MM pickup, as it might give you better results in different positions.
The point to all this, is to get your amp to a "close-to-perfect (for your taste)" tone and then use your bass controls to add or take away from that.
Hope this helped a little bit.