How to optimize sub integration with 2 channel?

I’m at the point of wanting to integrate a proper sub into my 2 channel system.

Hey folks,
I understand that I can control the gain and frequency of the low end of the sub,via the sub.

But is there a way to do the inverse? Can I reduce the low end of the speakers to about 45 hz and use
the sub instead from about 44 hz and below?

If possible, how would that work? e.g., use an external crossover for the floor standers?
The problem is that there is too much output at around 3-50 hz if I use both the speakers and the sub.

thanks!! Gary

Rig: (Bel Canto DAC–> PrimaLuna Dialogue HP tubed integrated–>
Dali Helicon 400 floor standers, Spatial M3 Triode Masters, and coming soon Dynaudio S3.4 Contours (thanks Joe)