Yes you need to cut or remove your bump stop. I'm not familiar with the Fk springs but most lowering springs do require cutting or removing it. You should check the springs' instructions to make sure. I had to remove mine with my H&R race.
Also what shocks are you using? Bilsteins and Koni shocks have adjustable height perches.
alright i cut my bumpstops in half b,ut i have to wait before i see the result because i lost a washer! now i have to wait till tomorrow night after work to put it back together.... bummer