Kelly,The best crossover point will be some what dependent on your room. For instance I have wood floors and some low frequnecy boosting problems because of theat. when I crossed at 80 with a 4th order, It still gave me too much around 100-150hz. I found the best point for me was higher than that. you will need to tune it in a bit. 80 would be a good place to start if you have carpet.
Bill