Using a pair of T9i RELs, connected via their high level Neutrik cabling. Corner placement per REL instruction.
These are the first subs I have auditioned that I can actually stand to listen to because they integrate so seamlessly with my Dynaudio floorstanders.
With my room gain, they measure flat to @ 22hz, but with visceral impact at 16 (I forget the measurement there).
They actually improve the imaging and lowest octave of my floorstanders, but I deviated from the REL guidance this way: I reduce the crossover point to the bottom of the Dynaudio's "flat down to" response (35hz), and increased the REL volume setting.
I am amazed at how well phasing works with the bottom octaves of the Dyn's - which is a significant problem with all other subs I have tried over the years.
Placement took a while - I used the Stereo Review test signals - but this was to get the loudest and most effective room coupling.
But with or without fine-tuning sub placement, integration with the mains was easy and surprisingly nice. Fine-tuning placement only extends the bass.
Other listeners comment that they are pleasantly surprised at the impact AND INTEGRATION of the sub. 2 channel or soundtrack.
They just augment and extend the bass, without calling attention to themselves.