Two crossovers points that are more than an octave apart are acceptable and no harm should be done. If the LPF was set at 100Hz and 24dB/oct then the signal would be 48dB down at 400Hz and wouldn't be audibly affected by a 400Hz crossover.Turning the LP to 400 doesn't defeat the crossover slope though only the crossover point. You need an on/off switch to completely turn it off. Not sure if using two slopes at the same time is good or bad.
RIchard, You should come to Arizona and help me tune this Audison Prima.Two crossovers points that are more than an octave apart are acceptable and no harm should be done. If the LPF was set at 100Hz and 24dB/oct then the signal would be 48dB down at 400Hz and wouldn't be audibly affected by a 400Hz crossover.
I agree that using the head unit for crossover settings is handy for listening to the effect and picking what you like most.