Focal loudspeaker drivers

There is absolutely nothing wrong with 4 ohm units, other than woofers presenting a "challenge" to be succesfully voiced in accordance with audiophile standards. Next year I am expected to work out a 3 way Focal based project; 11W; 5W, and Be tw.
 
What does that mean? What's a speaker's impedance's impact on the »voicing«? Frankly, I suspect audiophoolish babble here 🙄.
Btw, the Focal TC120 inverse dome tweeter is/was a very nice unit. It sounds well in the Focal Onyx pair that I've built when my elder son was a baby, about 35 years ago. Now this son owns and runs them to his very pleasure 😀.
Best regards!
 
My experience with the tioxid (TC90 if I remember correctly) was not very good. Sound was of damped metal cone but nothing spectacular but the surrounds (looked like some form of cloth) failed within 2 years. Basically first one and then the second de-glued themselves at some points.