@immathewj so you are right in your questions, we discussed most of it to death. But the big question is - regardless how I set it up, how it will sound. Sometimes less is more.
When I wrote high pass/low pass filter, I meant: external, sorry for the confusion.
I think my biggest confusion is the right crossover point, and whether I should have stuck with one sub.
I would have been inclined to live in the camp that wouldn’t try to integrate subs with good full range speakers that were capable of getting down into the low frequencies.
I understand. I guess the long story short, if I never tried, I would always wonder, what if....
Now that I tried, I understand that I need better components to take advantage of the sub, or I use little hacks. Human voice is above 100Hz, so I would think, if I filter out the signal below 100Hz to the mains, it still would be OK with vocals. I will find out soon!
This is what it looks like