Hey Matt -- Congrats on your subs! I've got the same coming, probably on a similar timetable. To go with m80s, not the LFRs though. They will be in my office for the next "little bit" until the theater room is done.

Its an interesting question. In my my case, and in keeping with Casey's comments, the placement will be largely dominated by the design of the room. Unless it just really doesn't work at all, the placement will be outside the screen, behind and to the outside of the mains, close to the front L/R corners. Corners are good for exciting all room modes & getting lots of output but potentially there are downsides as well. Potentially, the symmetry of this setup could work against this placement (mirrored excitation of modal points), but I will guess that some phase tweaking could help.

My impression of the newer Audyssey SubEQ HT module is that it first analyzes each sub's output separately (up to 2 IIRC) and then secondarily considers the question of how they interact . This could potentially be handy. In fact, here's an official quote I just found from their Q/A page .

Quote:
MultEQ XT32 is the flagship version of our technology to measure and correct room acoustical problems. Sub EQ HT is a method we came up with to deal with multiple subs. If you only have one sub then it's not in use. The idea is to first measure each sub separately, then apply delay and level settings so that the two subs are now time and level aligned. Then we ping them once more as "one" sub to derive the room correction filter.


Delay, phase adjustment, and relocation of the sub will have some overlapping consequences (with more or less similarity in the first two depending on the implementation (digital vs analog, say). Some interesting discussion on the difference between phase and delay here (posts 19,22,23 are insightful, among others) . I seem to recall a comment from Andrew that the phase is usually set correctly whenever the bass feels the "fullest". Again, I will guess that the phase dial might be comparably valuable to (and perhaps even more valuable than) physical relocation for tweaking the 2-sub interference pattern (possibly while retaining the benefits of corner excitations), although there could likewise be consequences to changing the phase relationship relative to your mains in the frequencies where they are playing together (crossover range).

My best guess to a starting point on the answer is this: place each sub where the sub crawl tells you to put it on its own. Then adjust the relative delay/phase to optimize the pair together (either by hand or with Audyssey, etc.). Disclaimer: this is a low experience opinion ... those with more experience might confirm or refute. In my case, the plan will be to place according to the room design (with the idea that corner positioning is generally good for output levels, at least), and then let Audyssey try its thing out.

Don't know if that helps, but interested in hearing your experience on i) the optimization of dual subs and ii) how the subs contribute the the experience with your LFRs. The residual benefits of a (near) full range speaker when you have a nice sub have been discussed elsewhere, and since your speakers are about as full-range as they come (and well powered to boot) the contribution will be interesting. As will Craig's upcoming "super speaker" M100 + EP800 experiment.

Cheers - DSQ