Anyone gone from a single REL sub to stereo subs?

I have a 17.5' X 14' X 8' room and was thinking very seriously of going from a single REL Stentor III [which I love] to a stereo pair for better imaging and pressurizing of my room. Has anyone done this and what was your opinion of the change? Improvements? Negatives? (other than cost)? Problems with placement or integration? Although I'd like to hear from REL owners who have done so, any information from other sub owners who went to stereo subs will also be greatly appreciated.
Phasing is more critical with subs. Both channels will tend to have similar bass information, because the original music will have been largely non-directional, i.e., present in both channels (reflected sound in the venue/studio). If your subs are separated by a distance equal to a half (or one and a half, etc) wavelength, they could be out of phase and their waves could cancel. One solution is to stack them. (Of course, this may not be feasible with the RELs because they fire downward and require a floor.) Drawbacks with stacking include loss of stereo imaging capability and magnet interactions if the magnets are unshielded. I have stacked subs and use VPI Magic Bricks between the subs to help shield the magnets from each other.
I have a friend who upgraded his system and now owns two (2) REL Stadium II subs. He was not sure what result a second sub would bring. Well, his system improved with the second sub and you can easily hear and feel the difference. These subs worked well with Merlin full range speakers. About six months ago, he changed to horn speakers and regardless, the REL subs worked equally well with both set of speakers.
I highly recommend going with stereo subs. My experience are with the REL Stadium IIIs. I started with a single and added the second sub within 2 months. As best as I can describe it, the sound of the system "relaxed" with the added sub. It's a subtle difference, but one that I find well worth the expense. Integrating the second sub wasn't twice as hard as a single sub, but it's at least 1.5x.

My room is 31' by 14.5' and the main speakers are M-L Odyessey.
If money isn't an issue, yes adding the second sub will improve the overall sound and can help integrate easier in a problem room. I went from a single Stadium to a pair. Have always found that using a stereo pr of subs sounded better than a single mono sub 13yrs ago when using stereo subs instead of the single mono even in the trunk of a car. As stated above the improvement is of a subtle nature rather than the drastic kind but worth the improvement if money isn't the issue. Go for it. You should end up with a more balanced integrated sound besides gaining the added depth. If the single Rel is working well for you and the math is on your side, I say go for it. All the best - Mike
. . . to take the Stentor plunge again. I am very happy with a single Stentor III but, many moons ago, went from one to two subs (in a system MUCH different and long removed from my current one) and vaguely remember the same subtle but worthwhile improvement. It just took your commments to shake out the cobwebs from this fuzzy brain of mine! Having been of the mind set for the last few years that subs "muck-up" the sound of full range speakers, I hesitated to buy the REL. But, crossed over at 23hz and with the coarse and fine tuning adjustments, this Stentor III really adds that last little ooomph way down below and it does it with musical punch, detail and without imposing itself on the woofers in my main speakers! Yeah, a second REL it is!!
I have two Stentors Twos. I used one for a couple of years and then upgraded and added a second one. The difference is incredible. You will have better imaging, seperation, and a more open sound feild. The difference is actually more like a speaker cable upgrade then just adding bass. I was amazed at the benefits and two is more then twice as good as one. If you can swing the extra sub I highly recommend it.

Then there is the bass. OH LORD. There is nothing like it.
Thanks for the encouraging post Perfectimage. I ordered the Stentor III today and am very much looking forward to the improvement!