Comparison of various subwoofers for 2 channel audio

I would drop SVS from your list unless you desire one note boom bass

That’s a misleading and inaccurate statement.  I have an SB2000 sub, and while certainly not SOTA it is absolutely not “one note boom bass.”  Further, there’s a member here who had both the highly-regarded Rhythmik F12 and SVS SB3000 in his 2-channel system and found them to be very close in performance to the point of being almost indifferent between the two, which certainly would not be the case if the SVS sub was that bad.  Personally I’d take Rhythmik over SVS albeit at a higher price, but categorizing SVS subs as “one note boom bass” is an over-the-top and ridiculous statement.  

I think I’m going to go with 4 dual opposed subwoofers, with the first 2 placed in a slightly staggered fashion just to the inside of the left and right speakers.

The easiest/most effective first shot may be to just place them in all four corners if possible as this is probably less likely to produce peaks/nulls. Better yet, put them at the midpoint against each of the four walls as that is supposedly optimal placement — that’s what I’ve heard from an expert anyway, and it’s free to try of course. FWIW.

It’s really hard to see going wrong with a couple Rhythmik F12G subs and along with your MLs should be quite something using all four.  FWIW, and best of luck.