The Audyssey rep is correct that you should use as closely matched speakers as possible for wides because they share a large amount of audio information with their corresponding main speaker.

I think the best wide speaker for Axiom towers is the Axiom M2. Those are what I use for wides with my M80v2 (2005) and they are a perfect match.

You could try to use another brand but there are going to be direct pans moving from the main to the wide speakers and back which will likely make any timbre difference noticeable.

3M80 2M22 6QS8 2M2 1EP500 Sony BDP-S590 Panny-7000 Onkyo-3007 Carada-134 Xbox Buttkicker AS-EQ1