So it looks like the top boxes are passive. so the system processor should be configured for stereo two-way. In truth, there are a few ways to deal with this. Refer to the manual for the C2402 and look to see if it allows this, or see if the crossover points can move either way up(to 20KHz) or way down(to 20 Hz). That would allow you to configure it as a 3-way, where you would only use the mid-high outs, or the low-mid outs. I would start with the subs crossed over around 80Hz(top boxes would get 80Hz and up).
Option 1: since you only need 2 ways from the C2402, if it can't be set as above, is it possible to set crossover frequencies so the the mid output is simply not used? IOW, the low out would be crossed over at 80Hz, the high out would run from 80Hz and up, with the mid out not used(in any case, you only need 2 way for the speakers you have). Its seems a bit like the system designer may have not chosen the best combination of gear
Variation: If you have other means of tuning the top boxes(like some third-octave EQ's at or in the console), you could feed L&R directly to the amp channels powering the top boxes. Then use an AUX send off the console feeding an input of the C2402 and set a single output for a sub out(to the amp and subs). Using an AUX send to feed subs is quite common
If none of this helps, its time to call in some professional help from a local audio expert
