I don't think anyone can say whether it will be an improvement since that really is a subjective opinion of the person who will be listening to these speakers.
That being said however, there can be a huge difference in using speakers that are all made of the same brand by a quality company, such as Axiom. The timbre matched speakers will sound alot more "together" in my opinion. I look at mixing and matching speakers like buying different brands of tires for each wheel on my car. They might all be the same size but each one will perform slightly differently which may not be a good thing.
I recently bought an Onkyo DS797 receiver and i am also in the process of deciding on the next set of speakers to purchase. Presently Axiom is the forerunner but the new Angstrom Modulars (http://www.higher-fidelity.com/index.htm) are also in my price range and a very well made speaker.
Angstrom does not have much of a website for info nor quick customer support like Axiom, and that sort of thing means alot to a customer like myself.
I say go for the Axioms and never look back.
"Those who preach the myths of audio are ignorant of truth. Research begets reality."