Thank you, Tang, as it might take me a while to set up a separate system thread, more so as everything else aside from Cessaro is rather basic with not much audio exotic(s) to recommend, and there are few, if any dedicated Cessaro threads around the global forums community.
I have spent quite some time looking for the best crossover point and slope, trying to cross as low -at 80 hz with -6db slope (as 1st order is supposedly better for phase (non)-inversion), moving up and down and currently settling at the mentioned 115 hz level and -18db.
Setting the crossover point below 100hz generally resulted in a perceived lack of energy at that region given that the mid-bass horn roll-overs pretty steeply down from about 125 hz or so.
Setting the slope at 6db while theoretically best resulted in too much low bass energy slipping into the mid-bass area and beyond, muddying up the sound...
A good practical technique if you are doing it by ear is to turn OFF your main amps and to listen just to the bass bins, how they work and resonate with your room, how you want the low bass to decay, where you feel you do not need the low bass energy any more.
Then when you turn the main amps, you can adjust the crossover point one or two 5 hz increments down while keeping or maybe slightly increasing the bass volume.
That worked for me without any instrumental measurement.
The ability to adjust the phase by 15 degree increments on either of the channels is also interesting but so far I have not found a technique which would give me a clear signal that I am doing the right thing and not just blindly turning the phase knob.