From Dr. Phil (Marchand), AKA 'the crossover Guru':

"The choice of the crossover point is a difficult one and often some trial and error is needed for achieving the best results.

With the 24dB/octave crossover a good rule of thumb is to set the crossover point at least 1/2 to 1 octave away from the cutoff frequency of the satellite.

Thus a satellite with a cutoff frequency of 40 Hz requires a crossover frequency of 60 to 80 Hz.

The subwoofer should then have a range exrending 1/2 to 1 octave above the crossover frequency. In this case, if 80 Hz was chosen, the subwoofer should have a range of at least 160 Hz."

The problem with bass management is that most have a 12 dB/octave high pass filter that is designed to affect sealed satellites which have a natural roll of of 12 dB/oct.

That combines to result in a 24 dB/octave slope which then matches the 24 dB/oct slope of the low pass filter that's applied to the subwoofer.

Most sats are vented (like your M80s) which have a natural 24 dB/oct roll off. With the 12 dB/octave filter applied, the result is a 36 dB/oct slope, which then doesn't match the 24 dB/oct slope of the sub. This results in less than unity gain at crossover, which causes a 'hole' in response.

This being the case, it is my own opinion that you should move the crossover point a bit closer to the sat's cutoff freq. when using vented mains (unless your pre/pro has the ability to change the LP slope, which the 950 does not).

In your specific case (M80), I would try a crossover of 60 Hz., as 40 is too low and there is no 50 Hz choice. Move up to 80 Hz, and compare the results to your ears.

With the center and surrounds, of course you should move the crossover up according to the F3 abilities of each speaker because 60 is too low for them.

Since there is no selectable 36 dB/octave slope for the LP filter, there is no solution to achieve unity gain at and around crossover.

Try 1/2 octave away from the F3 of your sats as a starting point, but realize that the higher points for center and surrounds will cause the sub to be more easily localized.

This, unfortunately, is the very short answer, but I hope it helps.