Crossovers slope meanings Theta Pre-Pro????

The Casablanca III HD will allow me to set the crossover frequencies for all 7 speakers. I can choose between three crossover types Linkwitz-Riley, Butterworth and Phase Perfect. After reading the manual it seems I should not use the Phase Perfect crossover as this crossover is best suited for subwoofers that can operate linearly up to the 500 Hz range. My JL Fathom 112 does not meet this criteria so I chose to go with the Linkwitz-Reily crossover. I then contacted each of my speaker manufacturer’s and asked them their recommended crossover frequencies. For example for my Nola Micro Grand speakers Carl recommended 40 Hz.

The Casablanca III HD allows me to further set the “slope” of the crossover by speaker. I just can’t seem to get my head around what it means by slope at a certain frequency etc etc.

This is the exact verbiage from the manual:
A Linkwitz-Riley alignment exhibits zero phase difference between outputs at all frequencies. Acoustically, this means that if the sound sources are in proper time-alignment, a smoother frequency response will be realized at the listening position. The Linkwitz-Riley crossover is only applicable to slopes of 12 and 24 dB/octave. A proper Linkwitz-Riley crossover with a 12dB slope should have the low pass portion inverted. This is done internally in the Casablanca III HD.

f) Set the crossover frequency in the submenu. If a suck-out appears (lack of bass energy), then try increasing the setting. If the transition to the sub becomes obvious, a lower frequency is
recommended.
g) Set the crossover slope in the submenu. Generally, the smaller the bass driver or the fewer the bass drive units, the steeper the required slope. A gentler slope (6dB, 12 dB / octave) is normally less intrusive and provides better blending of the main speakers into the sub. Some sub woofers can sound “tubby” with too shallow of a slope. A steeper slope (18dB, 24dB / octave) can provide greater dynamic range and clearer dialog.
h) Try both settings of low pass phase. The correct setting is the one that produces the clearest, most solid bass.

I understand that I can just listen to each selection and hear what sound best. I would just like a clearer understanding as to what they are talking about.

Thanks very much for your help.