Can anyone hear the difference when you add REL subwoofers when playing two channel

In my experience having dual subwoofers (left/right channel) has made significant impact on the sound in terms of bass extension, depth of soundstage, air between instruments, etc.  Having said that, it does take some time to get it right.  Things such as placement in the room with respect to your main speakers, phase, low-pass filter, and volume settings all factor in so they blend in nicely with your main speakers.  When all is said and done, you really shouldn’t know the subwoofers are there, beyond the apparent soundstage enhancements.  Before you even start configuring subwoofers in your setup, make sure you have optimal speaker alignment first as well as seating position (should be where you have smoothest/even bass response.  I don’t have the fancy RELs, but own a pair of Definitive Technology Supercube I subwoofers.  Bass response is 13-200Hz and clock in at 1500W (more power than I need).  I’m always a little skeptical about in-store demos as things are probably not fully optimized.  From my perspective, it’s all worth the journey for getting better sound.
Gorm 

I have 2 rel. this is how you set up high level input:
make sure the yellow and the red are twisted together and going into the positive left on your amp and the black into negative left, and do the same on the right outputs. Put the crossover about sixteen clicks and the low level at about 10 clicks from zero. Play a track w repeating bass line. Lorde “tennis court” is a good one.Tune one sub at a time with the other sub off. First flip the phase button and whichever way sounds louder is probably the in phase for your setup. Work the crossover back toward zero until you like what you here. Work the bass level back to zero until the bass level matches the speakers but just kinda extends the bass response. Do the same on the other sub.  You’ll have bass that is on stereo and match’s and extends your speakers. Look for better soundstage and clearly better bass and midrange. Listen to sympathy for the devil, listen to the bass guitar, you can hear the guitar 🎸 not just the beat but the actual instrument, you can almost picture the strings being plucked. You can mentally picture where in the stage the bass player ( Bill Wyman?) is standing. Now your all set.

You can also run LFE input on the rel in conjunction w high level. If you have a surround processor w lfe out, this will go into the rel and should only come on with movies that have an lfe track.

MAKE SURE that your not running high level out into the REL and LFE out into the REL HIGH LEVEL INPUT at the same time. The sub out or lfe out on your amp needs to be input on the rel lfe input, not high level or you’d be defeating the purpose of true stereo bass extension. 

I hope this helps 
-ak

@larry5729  I'm not going to bother going to the REL site to check but I would be highly surprised (to put it mildly) if the T9/i puts out 300 "class A" watts.  

See my post which is directly related:
https://forum.audiogon.com/discussions/kal-on-sub-integration-and-antimode

Audioman58:
Doesn't the SVS turn the towers in to boom boxes and throbbing bass?  Did you have the same problem I am having hearing difference when you add and subtract a REL subwoofers when 2 channel listening?  The dealer told me I am listening for the wrong thing, an added bass sound.

When I listened to the S3, I got on my knees and put my ear next to the speaker and it was not pulsing out the beat.  All it was doing was putting a steady humming sound.  Hard to describe.