Having experimented with different subs and arrangements in-room I can say with some authority that the results you get may surprise you. And it can go either way. My experience supports the fact that if a single sub is good, then two is way better, and not stacked on top of each other in one corner. While that gives you more output, it won't help control room modes and give you even bass response thru the room. Separate the two subs and treat them like they are stereo because bass is not monophonic. It does not mean they have to mirror image in terms of positioning but try running them on either side of the screen or tv out from corner along the front wall assymetrically and run some measurements. Keep playing with positioning until you are happy with the results and then do some DSP on the remaining peaks and you should be in pretty good shape. That second sub will even out the response and give you 3 db more sub output, helping perhaps cut down on low freq distortion a bit. Well worthwhile expense to add the second sub.
Experience with stacked subwoofers?
I have seen a handful of responses to posts mentioning stacked line array subwoofers, like the stackable Rel 510s. Does anyone have a stacked subwoofer array in their system and can speak to their experience? The marketing hype that Rel puts out about this has me intrigued. Their explanation as to why it’s awesome makes sense, but also I want to go beyond the marketing and hear about real experiences before I drop a bunch of dough on something like that.