So, one dual J coil pickup, four controls, mid-price 18v active EQ.
Are the controls;
1) Volume, Balance, Treble, Bass
2) Volume, Treble, Mid, Bass?
I would begin by checking the dimensions (no pun intended) of the control cavity. This may dictate what replacement circuitry will physically fit into the available space.
As stated above, the stock EQ system on your bass is +18v. This should provide more than enough headroom for normal bass work. The likely problem with the Treble cut/boost control is that its central frequency is set higher than you would like. (Check to see whether this is adjustable via micro DIP switches.)
The other possible explanation is that the EQ system is merely boosting such signal as the pickup can provide.
If your budget can stretch to it, I would be inclined to put your money towards the NYC Soapbar model pickup.