Wow... I had to read your post a few times to make sure I was reading it properly. What you describe is the classic "Axiom vs. something else" review, but normally the Axioms are the "clear, forward, vocals more defined, portraying each individual instrument etc..." speaker and the other one is the "muddy, confusing" one.
A couple of thoughts...
1. The M80s are more placement-sensitive than smaller speakers. Depending on the room, they like to be at least a foot and a half from the back wall or they can sound boomy (which might translate to muddy ?).
2. The salesman could have been fiddling the volume controls to make the Energys play a bit louder than the Axioms; only you can judge whether that is a possibility. Having said that, I don't think a dB or two would be enough to make the difference you described.
3. The switch was backwards. I would like to think this is true but it's not very likely
I don't know what to say. Something is wrong here but I have no idea what it might be.
