Micah, don't take this the wrong way, but there is not a chance in hell the M80's would be shrill to customers at the volumes and in the setting you are talking about. You are describing the most non-critical of listening, background music. You could use Bose, or even the brightest Klipsch you could get your hands on, and at 80db no one would ever call it bright. You might have a serious echo problem in that room that will be noticed, but you are not pushing the speakers to a realm where these problems will arise – if they exist.

If you have are concerned about your enjoyment at normal critical-listening levels, then perhaps the M60s would be better for you. They are more laid back, from what I have read, but sound great according to comparisons to the 80s. I guess I'm just having trouble rectifying your heightened state of concern with the described intended use. I would say, for non-critical listening, it is damn hard to find a bad speaker at $1,000 a pair. It's like someone asking you if they are going to hate riding around the neighborhood on a motorbike you consider to be pretty ordinary, but has significant performance issues at the edge. If they are never getting anywhere near the performance edge, it won't matter. Same with speakers.

And I don't own Axiom fronts...this is just my experience with good to outstanding speakers over the last 15 years. You are in a safe place. But if bright concerns you (and in your room I can see why it could!), try the M60's first.

Finally, if you frame your own pics in the gallery, you can use them as absorbers/defusers. Just try to get them away from the wall a bit (a few inches) to add some space between the wall and the pic surface. Then put fiber board or other absorbing material behind the pic. You won't see it from the front, but you will get some acoustic benefit. You can alternate between dense material and loose to get diffraction where desired. I've done this in my room and it works ok. The surface will reflect more that a pure acoustic treatment, but yours is not an audio room so just look for benefits where you can get them. Glass on the front will bounce it all back. But, perhaps, put a tall plant in the corners, add some accent screens or seating to help break up the echo of the square room while staying the functional side of acoustic treatment. Every item you can put in there will help the echo chamber you are dealing with. And that echo will enhance brightness, so again, consider the M60s.

Best of luck to you.
P.S. '80's rock will also enhance brightness (screaming guitars and banging cymbals, etc.) Bring CDs you expect to use with clients.

Panny 3000 PJ, 118" Carada, Denon 3300, PS3, Axiom QS8, PSB 5T, B&W sub, levitating speaker wire