What hz passive crossover should i get for my 6x9s?

i have 2 rockford fosgate punch 6 x9s and i had just used the one that was on there to go on the positive wire so it was a cheap solution for a crossover but when i turn the bass up on songs with a lot of bass it distorts a lot so im thinking ill just buy a crossover designed for it so what hz should i get for strictly highs? the crossover that was on there is a tiny black cylinder lookign thing it was used for the mids and highs in the middle of the woofer part