Short List of the Best 20K Speakers

I'm looking to pickup a pair of pre-owned speakers that originally sold in the twenty thousand dollar range and can be had for around half that today. I currently own Revel Studios. I love them but want something that can go below 20 hz while still maintaining all the goodness these speakers provide. I've already heard and liked Dynaudio C4, Revel Ultima Salons (original) and Eggleston Andra II's. It's hard to get a real feel for what they sound like in your home with your equipment. Curious to hear from people who have owned or auditioned any of these. Also feel free to add any you would like to recommend. My amp is a Krell FPB600c. My room is unfortunately a 20' square with 8' ceilings. I have echobusters placed all over to keep the soundwaves from pretending to be pinballs in a pinball machine.
1st, Enter 'room mode calculator' in Google. The lengths of sides being 2 1/2 times the height is awful, not to mention the room being square!

2nd, In this case the room is really your enemy. Spend some time and money on the room. If the total budget is 20 large, apportion some of it to getting the acoustics fixed. Do that at the same time you install your stereo.

Finally, 'Add a sub' is probably not advised at this point. When I did as I suggest in point #1, so many frequencies popped up that were even, or near even multiples of 20hz that I can only imagine the room as a big, vibrating echo chamber.

You can put 20 large in speakers only, which is 2x what I have in my entire, reasonable sounding system, add another chunk into electronics and a GOOD source and still have unsatisfying sound. Before you get on this merry-go-round, consider your room.

I'll bet your EchoBusters are some of the best money you ever spent! Low Frequencies are the absolute worst!
Spend the money on improving your listening environment if you really want to (it's a free world), but real 20Hz with decay for ambience is going to be extremely difficult with the dimensions of your room. And why? Most music has little to no first order 20Hz cycles. Are your trying for "Dafos", organ music, HT action movies? There's so much good music out there without 20Hz and trying to keep this particular parameter is going to be a money sink where you'll just piss it down a hole.

I've done it; Double Entecs, Maggie IV Bass Panels, Pow Wow. I never got it right to my ear and even turned those subs off during all my regular listening. Honestly, IMHO a well balanced music system with 20Hz bass is not in the cards for $20K.
I just auditioned (again) the Devore Fidelity Reference Silverbacks. It is getting more and more difficult to not pull the trigger on these incredibly musical and beautiful full range speakers. They sell for around $17000 new but outperform a lot of speakers costing much, much more. Definitely worth a listen!
I had the original Revel Salons for a long time. I sold them and I will get the Thiel CS3.7 in a little while. I think The Thiel is an incredible sounding speaker. I may not go down as low as the Revel Salon but i think it sounds better overall. I would also consider it an improvement over the Revel Studio.