Need help design active crossover circuit
If you don't already have it you can download the TDA2009 data sheet here Datasheet.  

The input to the amplifier is not a differential amp.  So you need C4 and C5 to prevent changing the internal bias.  If you look at figure 12 in the linked data sheet you will see that putting 12kOhms to ground on the pins 2 and 4 will cut the amp off.  That is why C4 and C5 are needed.

The data sheet already provides a circuit for doing an active crossover before the amp.  it is shown in figure 15.