With no disrespect intended to those of you putting forward various proprietary solutions for sub set up, I use the ultimate power in the universe for such configuration with my 3.5s - a pair of ears.
Not scientific, but my goal, as I’m sure applies to all, is to create the sound that best works for me musically, not technically.
As I say, not wishing to put down other solutions, but I really can’t see how ears can be beaten.