If don't have a global crossover why not set the fronts to 60 Hz? They are +/- 3 dB down to 60 Hz so you might as well take advantage of that. I have found that with a crossover of 80 Hz and only one sub that I can sometimes locate where the bass is coming from in certain movie scenes (only occasionally). If if is possible to lower the crossover of the fronts then this might help with this problem.

- Nick