Bob, nice to see you here.
I didn't know about your setup/room placement issues, so with that in mind it could certainly be some crazy room interaction that you're hearing. Also, you're going to want to check the receiver to make sure certain EQ's aren't enabled. I haven't used a Denon in a while, but be sure all EQ is off and that the tone adjustments (bass and treble) are flat (zero). If that doens't help you can try running Audyssey EQ (if the Denon has it) to see if it helps with the thin mids and brightness, but I am not a fan of Audyssey so who knows...
As BRM said, pics would be most helpful. With the speakers being so close to the walls, you're bound to have reflections, and while I do think Axioms are a little bright even under ideal conditions, the reflections may be amplifying that sound.
So have you set up an appointment to audition the ST's? In comparison, the SongTower's have a lush, detailed midrange. It is big and full, unlike the Amiom's thin and small presentation. The top end is also more refined, especially if you listen to the ribbon version. Instrument timbre is more accurate, as is sibilance. To my ears the ribbons are more accurate to the real thing (live music), but the domes on the QWT SongTower's are one of the only soft domes I've ever liked.
Hope that helps. I hope your situation gets resolved and you find a speaker that will bring you years of happiness, even if it's not a Salk product. Best wishes to you!