I think your best bet is,
not sure what mixer/desk you running firstly but run the CBe18 from your mixer straight to your crossover unit then use the Sub woofer out of the crossover unit to your CBe18 amp........maybe if using the CBe18 as stand alone Sub you can go lower between 80-90Hz. Then just run the Mackie thump as it is ie. straight from the mixer....You dont need to run this to your crossover unit anymore as this is all pre wired inside hence fullrange meaning you cant separate your mid and hi unless you disable the wiring inside and do another wiring and use your Active crossover
....But there is no point as looking at the crossover unit can only go up to 7Khz ?
. Might as well just use the Mackie as it is.
CBe18 say between 80Hz-100Hz then set Mackie low freq to meet your Sub...That way your not losing anything or having a gap in your freq. Mackie 15's will just cover the Kick section to Mid while the rest will get cover of Mackies Hi. Heard them a few times and they can certainly thump.
Or play around with the Sub freq on your Crossover unit until you think which sound best for the CBe18 and set Mackie freq. accordingly......CBe18 can certainly go higher than 100Hz so just a matter of if you like the sound over that.
Are you running the 2 CBe18 Left+Right and Mackie on top of each of them?....or using the 2 CBe18 mono in the middle of the 2 Mackies?