Some people remove the bumper support(which you've dubbed the "cross bar"), which I don't recommend doing. Your other options are to trim the bumper like you said(I'd recommend that), or you can take a plasma cutter and notch out your bumper supper. Option #2 is the safest/easiest way to do it. Use a cutoff wheel and a grinder. Or failing that, a Dremel. Take your time and make your cuts as straight as possible. It'd probably look best of you removed an equal amount of material all the way around the opening, as opposed to just notching for the bumper support. After the kit is painted, you can paint the bumper support black so it'll blend in better.