I will try a AC filter if I can find one at a decent price.

at the price of losing my warranty unfortunately.

After further reading about filters I ended as the same conclusion as you. I first thought the L2 was removing high frequencies, but it is in fact an LC filter to remove bass more efficiently.

Will I get the high frequencies back if I remove L2?

That’s my question, how do I get rid of the crossover. In my limited understanding of electronics, the c3 capacitor will do nothing if terminals 11 and 12 are open. I’m not sure though.