driver phase question in tri-amp using 18db/octave

I'm a little bit confused.

I've just purchase two stereo active crossovers. One is a Threshold PCX and the other is a Bryston 10B std. Both units are 18 db/octave filters.

So I'm confused how to keep all three of my speakers in proper phase. In hind site I think 24 db crossovers would be easier but my objective was to use crossovers with discrete components and eliminate integrated op amps which I believe degrade the sound somewhat. Other than tubes the only 24 db filters I could find use Op amps.

So I would run input to one of the crossovers (not sure which one to use first in the signal path yet) and then the high pass right to my high frequency amplifier and then the low pass from that crossover into the input of the second 18 db crossover. Then obviously the high pass from that crossover to my midrange amp and the low pass to my bass amp.

Would my midrange phasing be all mess up?

The Bryston is adjustable between 6, 12, or 18 db but I still feel the steeper 18 db slope would work best for me.

Any advice greatly appreciated. thanks!