And now that it’s moved to the correct forum (it’s Digital DJ Gear not DJ Booth 🙂 ), to the task of answering the OP.
If you buy an active sub that has a built-in cross-over and stereo input and high-pass outputs it’s relatively simple:
Mixer with two balanced signal cables to the inputs of the active sub.
High-pass outputs from the active sub to the amp with balanced signal cable.
Amp to passive top speakers with SpeakOn cable.
Any other way to set it up is a waste of time, money or both imho (like getting a seperate cross-over and another amp/passive sub combo for example).
You can not feed a SpeakOn cable into an active speaker (the connector isn’t even there). SpeakOn carries a sound signal already amplified from an amp to a passive speaker. You use a (preferably balanced cable) to bring a signal from mixer or controller to your active speaker. That has the amp built-in.