Rick,
You might want to double check and make sure your speakers are in phase. That can give you a very dull sound if they are out of phase. A passive crossover like the other guys suggested is a very good idea. The way I run my systems is 3 way. I run my sub at 70 and below. My Morels in the doors run 70 and beyond. Morel mid is so damn tight. It just slams you hard. I have ribbon tweats, and they are great sounding spappy highs.
I would not use the crossover in the deck, I am not to fond of doing that yet. I still like the good ol electronic 2 or 3 ways.
Hope that bit of info helps you
Kynan