My system came together in three chunks.
For Christmas of 2003 my wife 'surprised' me with the VP150 and a pair of m22's. A pair of Energy Take 5's and a Kenwood sub held down the rest.
In the Spring of 2007, I surprised myself with a pair of M80's and an SVS sub. M22's became the surrounds.
And recently, I bought myself a pair of QS8's. The M22's are now doing time in our bedroom as a 2-channel system.
Whether you do it all or slowly depends on your budget, what you want to do, and what sorts of speakers you have lying around.
If you're going for a full-bore 5.1 setup and you already have decent other speakers, I'd say it's perfectly fine to do it a piece at a time. If you have no other speakers and are starting a home theater from scratch, you might as well do the whole thing at once.
You never know, there are a few oddballs out there that don't like the way Axiom's sound, and it's a lot cheaper to return a pair of M22's than it is a full 5.1 system.
