low bass response

I would measure the room. Can just be test tones streamed and a simple DB meter. 
 

The only other thing I would add is distances between the front and side walls. You really need to be below 39” or over 7’ not to cancel out the low bass. This is due to the wave length at 1/4 of its length. Anyway try moving the speakers closer to the back and or side wall (driver less than 39” and less is better to not cancel low bass) and see what happens. Avoid the side wall and back all distances being equal. 
 

The revels have plenty of bass (I am a fan) but it is a little flat in the bass for my tastes. I personally run 2 subs regardless of the chosen speaker. I have yet to hear a speaker where high-passing the first octave (63hz and under) does not improve the sound. 
 

You don’t need room for bass but you kind of do…, I mean headphones make good low bass with zero distance but you hear the direct wave.  A 20hz wave is 54’ long and will bump into walls, bounce back and cancel itself out. Like two baseballs coming from different directions and hitting each other. 

35hz is 32’ long so the 1/4th wave will be 8’. 1/4th wave matters as because once it bounces off the wall and comes back it is a 1/2 wave and 100% out of phase with the first wave. 
 

That is 8’ from the acoustic center of the 3 woofer and port combined. So your ceiling will be canceling the bass at 9’ but the side and back walls will not be. They all sum together.  Anyway I would just move the speakers around a bit and see what happens. Closer to the walls for more low bass. Same goes for your seat. 
 

In a domestic home I personally think subs with DSP is the only way for flat low bass.