Room Treatment Question, lost the lowest bass notes.

This is what I have:
25 x 40 ft room 12 to 15 ft tall ceilings

The stereo is on the narrow wall on one end of the room. (I can move it 90 degrees if needed).
I have a pretty good system, Wilsons, Audio Research, VPI, I do not think I have to give what components are. They are considered high end.
Here is my problem.  My seating position is about 15 ft away from the speakers.  The lowest notes that I know that are on the recording are NOT being presented. For example: Lyle Lovett - She has already made up her mind.  There are a few super low notes on the song. I have heard them before when I had a lesser stereo.

I did find that when I stood near the open door at the far end of the room, I can hear them. But when I move towards the center of the room near the far wall, They go away. It is very easy to hear the drop off.

I spoke to a couple of HiFI shops in the LA area. One mentioned a Node Cancellation. I do not know what that is.
I added (2) 2 x 4 section of sound absorption material high on the back wall. The only conclusion I came up with is the low notes are being cancelled once they bounce off the back wall and head back to the front wall. Stop the bounce and the low note have a place to go.

I am thinking correctly here or am I just reaching for straws, and I am. 

I am no scientist. Please answer in non scientific terms.

Thank you. 

That's why I'm looking forward to checking out Mike Lavigne's place this weekend. Some audiophiles are coming up from Portland. First stop my place, then on to Mike's. Kind of like a pub crawl. Heh.  

My room for sure has problems. Had a friend over a very long time ago, Holly Cole hits this one note and its just crazy overload loud. Told my friend sorry its the room I'm working on it. He says no way she just overloaded the mic. But I knew better. The corner tunes you can see in my system pics virtually eliminated this resonance. Cleaned up some other stuff as well.  

That like I said was a very long time ago. Like at least 20 years. My system is a whole lot better now. Room problems that back then blended in with other problems now stand out as room problems. To me anyway. Everyone so far thinks the room sounds great. Better than average sure. But not great. Mike Lavigne though, now THAT'S a ROOM!  

Bet your bottom dollar my eyes will be peeled every bit as much as my ears will be taking it all in especially looking for ideas to improve the sound in my room.
Problem is your room dimensions are conducive to suck out at a lot of low frequencies. Best short term benefit is listening position location. Which needs to be between two nodes one about 25Hz and another just over 40hz. I estimate you will want to be 16 feet from the front wall for best response.

Look up AMROC on the web and work it out exactly.

Lots of good suggestions for optimization in the thread.
Thanks for the reply's. 
I am not adding any subs. I got enough money spent on equipment, $45K.
I could spend money on having the Wilson Tech come set speaker placement. 
I have my seating position at 16 ft away from the front now. I could move it back a few more feet if needed.
I did shift the center of my speaker center to the right about 3 ft. That helped. I have a brain fart with the initial speaker placement.

I also added (2) 2 x 4ft sound absorption panels on the back wall and (2) 2 x 2 ft panels behind the speakers.  

Time to let my ears do the judging.  At this level of HiFi.... It is all in the room now. 
I had great luck using Vicoustic Extreme Bass corner stacks. These won't overdamp, just sound better the more you add. See my systems page.
@bill_peloquin, The 'Wilson' setup is demonstrated (somewhat) in a video by Wilson.
The process described begins with finding a 'neutral zone' and this can be best demonstrated with an assistant vocalizing a sentence / tone (an octave or  two). First against the wall and then moving into the room five inches at a time (or less). Until voicing (literally) sounds normal (like outdoors).
One note: Vocals is only one third of the audio spectrum.
Highs and lows also need to be addressed separately.
Also finding the correct distance between L/R (mains) is significant.
I would suggest that the distance should be one that gives the best perceived power for a given volume (same).
Set up the Mains first without the Center Channel.
Integrating the Center Channel afterword should be easy especially if you are able to adjust in the time domain.
Also notice that there is no 'room treatment' shown in the video!
The Wilson line would be a baffle less type design (generally) with a more uniform radiation pattern.
Once a zone (for placement) is located fine adjustments (inches / cm) can be made. Toe in as well (a further discussion).