Hmmm....with no source listed, I guess you listen to the radio in 5.1?
I would think that you should be fine driving the Axioms with your Pioneer. If your rear speakers are that bad, perhaps you can rearrange your models when the new front models are installed. You might look to get a balanced front and rear set from Axiom, with M60's and save some money for the rears. Have a look at the Factory Outlet models, as most who have purchased them have had good results.
Only your budget and current satisfaction can guide you.
