REL will go lower but you can save a few buckjs and get a Vandersteen 2WQ one of the great bargains in hifi.Uses unique x-over ste upo where you don't hokk it up line out but combine it with speaker wire taps and itn reacts to full waveform.If you want a Home threatre sub all you need is "boom in the room" the bigger the beter wityh a servo amp doing a beter job.But REL.Vandersteeen,(and above you price point) Martin Logan Descent a set which uses multiple small drivers to equal one big one.To get speed ,pitch accuracy etc your talking $3K and above to move large 15" and 18" drivers in Ariels,Revelss,New Velodyne DD series etc.This means it's fast and lithe enough to be pitch accurate and it's speed allows it to be matched with most demanding speakers including planar's like Maggies (great combo with 1.63.6 with aforementioned) or lectrostatics like Quads where the speed allows pitch accuracy and easiset blending for 2 channel systems.You can get 35hrz +/- 6 db out of Vandersteeen and more depth out of REL out of two into models on used market fpr another $300+/-.
Chazzbo
Chazzbo