What happened to my room acoustics

A suggestion, I start with math for positioning my woofers (Cardas formula) which in your case will be approximately 6.25' from front wall and 3.8' from side walls.

I would then start sitting (on a chair on casters) at a perfect equilateral triangle and roll back (away) from the speakers slowly which will help you find several "semi sweet" spots which you can focus on later on when fine tuning.

Of interest is that you mapped out the "golden triangle" and then didn’t adhere to it.

Thanks @aewarren & @ervikingo. I experimented with that a while ago. If you take a look at my second sketch, you’ll notice the ’golden ratio triangle’ where 0.448W and 0.276W align exactly with your numbers. Unfortunately, I’m not fond of this arrangement. Firstly, it utilizes only 6% (17 square feet) of my entire room space (280 square feet) for the listening area within the equilateral triangle. If I place my Poang chair with an ottoman in that listening position, my feet would almost touch the speaker plane. It feels quite cramped. Secondly, I found the speakers and stands to be extremely intimidating. I didn’t enjoy the setup at all, and I couldn’t sense a spacious soundstage in such a small space. I must admit it’s a setup that I find rather impractical. I apologize for the strong language, but that’s my honest feeling about it.

@lanx0003 No worries, those are suggestions.  They have worked well on my 4 prior rooms and speaker setups.  

The most challenging were the Aerial 8b with the side firing woofers and the Betas since you have further flexibility but I had already placed a huge projection screen which can't be blocked.

BTW, like the Poang but its a bit too upright for my back.

@ervikingo  The almost full-range Aerial 8 is reviewed favorably with impressive specs. It could be an endgame choice. Good luck with them. The Poang chair is a bit too upright for my liking as well. But if I sit further tilted back (on other chairs), I found that the sound perception changes drastically.  I am getting used to it now.

@erik_squires @newbee @mijostyn @rhljazz @hilde45 @audiokinesis @ervikingo @jamesw767 @aewarren @ronboco 

Again, thank you all for the insights and great suggestions. I think I may have found a potential solution for issues I am having. The Anthem Room Correction (ARC) system seems promising. A gentleman had the same 12kHz dip issue in his Buchardt S400 II speakers (so I guess it's inherent to the speakers) and he was able to correct it with the ARC built into his Anthem STR preamp (>$3k). I don't plan to purchase that expensive preamp, but MartinLogan has a Unison preamp ($199) with ARC built in. I hope it will do the same trick to address my issues. Fingers crossed for it.