Am I done yet? LOL

Often times bass response issues are because of room nodes which can be corrected by dialing in the peaks in the response. 

Agree with @jrareform you may be sitting in a null. Bass is tricky and if you have yet to crawl on your floor (military crawl), you will know what you are missing if and when you find it.

You may want to start with placing your speakers straight ahead (no toe-in).

Not knowing what dampening material is on your first reflection point, but 4-inch would be recommended- preferably with Owens-Corning 703- and not foam or most of what one gets from GK or ATS and others.

You may also want to try the diffusers you have on the back wall and place them at the first reflection point, or just underneath your current first reflection material. 

@goodlistening64 Take a look at the picture in my profile. I know about treating a room. I've been doing this for around 50 years :-) I've already done the things you suggested as I've been working with this room for over 3 years.  

On the side walls is ATS 2" thick. Behind the speakers are ATS 4" bass traps, In the corners, GIK Bass traps. 

I did just order a second SVS Evolution 5000 sub.

@traudio 

Accuphase....although I've read they are on the soft and romantic side which wouldn't suit me. 

This is so not true. You can go through the Accuphase thread that I started. I was hesitant about the Accuphase, especially Class A models. That "warm" sound is completely misleading. I found this out after purchasing the A-48S amplifier which I have been thoroughly enjoying since Dec-2025.

If you get a chance, I suggest that you try to listen to an Accuphase amplifier. It would be a time well spent. Good luck.

@traudio 

I did look at your room. Your room is 28' x 13' and two 15" subwoofers will overpower that room with pressured sound levels making it impossible to achieve a balanced, un-distorted response.

If you have issue with others providing insight in order to find a remedy, then why start a thread to highlight that fact? I am not attacking you personally, but bringing up the elephant.. which is your room! 

Your room has a width bottleneck, a height challenge, and raising sound pressure levels to the room by adding a second sub as a solution is going to put you where you were with the 888's. 

I’m done.

And I’ve given up golf, too.  It got to the point that there just wasn’t any challenge to it any longer.