I did go with the Speakons ... and I can now see why you recommended them.
We are planning on soon adding a powered subwoofer, front and center. (EKX-15SP). We plan on sending the signal from an Aux on our SoundcraftUi24r (and linking it to the master slider).
Our goal is to run our bass through the new subwoofer instead of our FOH speakers.
The bass will still need to go to the main FOH speakers to get the mid range/hi end definition, bringing up the aux feed to the sub brings in the needed low frequency content.
That is the same for any inputs that needs low frequency enhancement.
The aux for the sub feed should be set post fade.
The main FOH speakers should be high pass filtered at around 100hz, set the sub woofer low pass frequency accordingly.