Instead of buying a heavy-duty crossover you could just install small chokes on the front speakers that eliminate all freqs below 80, or 120, or whatever you want the cutoff to be. These are only a few dollars and are a simple way to crossover in a non-dynamic enviroment, where you do not need to adjust the freqs at all. Talk to your installer about getting these installed, it should only take 15 minutes to install on both front speakers.