Room Acoustics, minimal treatment and measurements

Yea closer to wall or even corners will boost bass but could also negatively impact imaging. Try it and see. If not then this may be a job for a proper powered sub or two. Gotta get that bass for best results.  Could be the speakers are just not fully up to the job  for a room that size. 

Are these older speakers that have been around prior to your involvement? Always possible woofers are damaged say detached from voice coil. Hopefully not. If you apply some pressure to woof near center while playing does it suddenly pop to life? That’s an indicator of a detached voice coil.

@mapman I really think his system would benefit most from two subs like you noted.  That way he could enhance low level listening, get proper music reproduction, and NOT introduce issue while maintaining all the better aspects.  He's very old school that 'subs are of the devil' and totally useless, but there are so many aspects of the music he loves, that he has no idea he is missing out on.  My understanding was that these speakers were made and shipped during the very early stages of Covid, so it took awhile to build.  I did some basic phase testing and the woofers are working and moving in the right direction, they are just at a much lower level in comparison to the mids-highs. 

@erik_squires I was wondering myself if this is one of those rooms/spaces, speakers and systems that would be perfect for using Bi-Amping?  I honestly never knew of "active or passive bi-amping"?  My step father had given me his old Adcom GFA-555 (modified) that I bet would be PERFECT to be used just for the woofer end, and leaving the Rega Illicit for the mid-high which that amp excels at in general (details). 
As we noted, honestly a couple moderate subs would really change the whole presentation, while keeping the amazing staging and details.  Alas, that likely aint gonna happen!  But at least I learned a TON from all of this, and it has made me appreciate my baby system in my own house, that sounds just as good as this does (just NO WHERE near the same staging!)  😆

Yes if teh speakers are operating properly then your measurements indicate teh speakers need help with the lowest octaves in a room that size.  Also yes he probably does not realize what he is missing.  Adding a powered sub or two properly almost always helps complete the entire musical experience even in scenarios less bass deprived than this one.  Cheers!.

I was wrong btw, I found I think a polish sight that says the min impedance is 4 Ohms, but still, with bi-amping you can set levels independently. 

The site also noted poor off-axis integration, a potential sign of the effects of the overlapping woofer/mid-woofs, so I really think at the very least, bi-amped with an EQ in front of the woofer amps is going to give you everything you need.

Always a good idea to make sure the mains are operating properly before adding subs. So if bi-amping with EQ is what is neded for that, definitely do that first and see where you land. What make and model are the speakers again? If they turn out to be too problematic in that room at some point, it may be time to look at alternatives that might be implemented to their fullest more easily. It really all depends on what the end goal is. Also of course how much time and money you are willing to invest.

Also I would say that you are starting out with a much larger than normal bass deficiency.  Can optimizing the speakers alone resolve that?   Probably to some extent.  THen from there its a question of is that good enough or time to add powered subs to finish things off.