why go against REL setup recommendation?

The most useful recommendation from REL is the level...if you do stick one in a corner just don't crank it up. The "sub bass" description of RELs is silly...they invented this term for reasons unknown as these things work EXACTLY like every other sub with adjustable crossover points. 40hz? 120hz? Whatever...silly...I use 2 RELs at around 58hz or so to blend with a pair of Heresy IIIs and one (a down-firing Q108MKII) is about 2 feet behind the left main speaker in a little corner created by a gas fireplace, and the other (Q150e front firing) is moveable near the right speaker...I move it a little away from a corner because I can...I slide it around (vinyl "spikes" don’t scratch the wood floor) based on what I’m listening to, or my mood, or relative humidity (which is the humidity of my relatives). Crawling around the room has nothing to do with how your rig sounds in the "sweet spot," so listen from there unless you like to hear things while crouched in the corner, and since all recordings are a little different, turn the subs up and down a little when needed (I stuck "chicken head" knobs on the High Level pots for this). There ya go!

I also use a REL with Heresy III and they sound great together.   You can NOT use RELs Neutrik connector wth fully differential balanced amps like ATI or many oof the amps they OEM for because they too are fully balanced.    

I have a pair of PP mono tube amps and I can't get a diffinitive answer if connecting the REL cable is safe or will deliver both channels so I have just used my Veledyne SMS 1 which I prefer because I can experiment with low pass, slope, and manual or auto EQ.    I have the R-305, it older but still sounds great.  I have it hooked to the LFE so the sub is not using it's x-over

The biggest improvement I can suggest is a isloation platform like the Auralex Sub Dude.    Unbelievable improvement in a room with hardwood .

Holy zombie thread, Batman!