Golly. I'm really sorry to hear that you're still not getting the results that you're after
As you can hopefully tell, I've tried to address as many potential causes as I can. One more though...
You wouldn't happen to have your AV Receiver plugged into some sort of surge protector or "power conditioner", would you?
I ask because I had a long conversation on another forum a while back with a fellow who was having some similar issues to yours. He was using the Ascend CMT-340SE speakers, as it happens. He was getting what he described as a very "tinny" or "shrill" sort of brightness, and the same sort of highly localized sound that I believe you are describing. He wanted his speakers to "fill the room" with sound, which the CMT-340SE certainly can. But he found they were sounding "small" and "closed in".
He actually had one solid wall on the left side, and a big opening to another room on the right - so a very similar sort of room layout to yours, in fact!
Anywho, we went through some very similar ideas and recommendations. But what I hadn't known when we spoke was that he had all of his components, including his AV Receiver and subwoofer all plugged into a surge protector. He eventually moved the subwoofer to a different electrical outlet, and nixed the cheapo surge protector in favor of an APC unit with "high current" outlets that I recommended.
Voila! The sound completely transformed for him, and sounded the way I know those Ascend speakers should sound! Only explanation is that the surge protector he was using was completely choking the electrical current being fed to the AV Receiver and other components. Moving the subwoofer to a different electrical outlet and swapping out the surge protector were the only changes he made, so that's the only explanation I could come up with. And it's quite common for surge protectors and "power conditioners" to choke the electrical current, so it's not out of left field.
Anyways, I bring it up, simply because what you're describing reminded me of that fellow's situation, and how he was having similar problems that wound up being an electrical supply issue. You definitely have good speakers and equipment, so you ought to be getting better sound than what you're hearing. As I say, the room acoustics can make a pretty big difference, but not to the level that you're describing. That is something else.