Have you tried Axiom's
Hearing Things forum? There is a list of people willing to audition. If there is nobody close to you in the list, try posting on the forum to see who responds.
I would describe Axioms as having a very clean neutral sound. I am very happy with mine.
I have no experience with the VP100 center as I am running dual M2s in my system.
Any of those receivers will be just fine. Pick the one with the best features for your folks.