Crossovers are subtractive, in every sense. They remove signal from the speaker. Good speakers will suffer less from this, but simplicity in the signal path is of prime importance.
Another issue that cannot be over stated is matching speaker size to room size. There are basic mathematical formulas that will tell you if there is enough room volume for the low frequencies to bloom, or if they will collapse. Big, floor standing speakers need a big room (if you're wondering if your room is big enough, it's not) to sound their best. Smaller speakers with less bass will sound better in a mid to small sized room. As a rule, smaller is safer, but you loose the cool factor.
Floor standing vs monitors is less of an issue. There are good full range monitors and there are good restricted frequency speakers that are floor standing.
It doesn't matter how good the gear is, or how good the speakers are, if they are too much/big for your room THEY WILL NOT WORK. Ego is a great motivator when it comes to buying speaker, but his sister prudence is much the wiser.