Attached are a schematic and an image of back and front of the circuit board. Interesting how the woofer is not filtered but runs from the "W +" to one end of Caps 1 and 3. The opposite end of these two caps are negative. The particular board is from an SP1700 but the 1200 and 2500 are the same circuit board with the same 700/6500 cutoffs. The only difference is Cap 3. The 1700 uses 3.3uF and the 2500 uses 4.7uF, etc. I also can't figure out how the switches work. L2 and L3 appear to be resistors? C N S stands for Clear, Natural, and Soft switch settings This thing is telling me the sluggish old OEM woofer can be changed and won't effect the crossover frequency range.