Subwoofers that do both L/R & LFE simultaneously?

Running a 2 chan/HT combo. I understand the REL subs allow you to connect both the stereo high level inputs and an LFE cable and the unit apparently senses the signal. You send the sub a full range signal. Any others do this? My Para s8's don't really need help on 2 chan, but it makes sense to me to use a REL type setup with the sub crossover at around 30. That way I get a little fill-in as needed. Am I missing something, why aren't all subs done this way. Thanks, this forum is great!
Nrenter, what you describe is technically the same circuit as I describe (except tied together at the amp instead of at the sub) And it's a little better, yes, for the same reason bi-wiring can be. But with the scheme you describe, you could really be buying lots of speaker cable!

Either way, the sub is sampling the amp output through a filter circuit of it's own. I guess that's OK, but being the stickler for cleanliness and simplicity that I am, I insist the sub have its own direct line-level feed out of the preamp.
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REL Strata III have another advantage in the sense that they are sealed enclosures which integrates well with any speaker in the chain. I use it with the LS3/5a as well as Kef Reference Two, both totally different speakers yet the REL seamlessly integrates with both and sounds superb.

I reviewed it earlier at A'gon for those who like to read it:
I like the way these sound.

Sorry, Nsgarch. I thought you were implying that the signal was rolled-off (via a low-pass filter in the sub) before being sent to the main speakers. As you know (but for those who may not) this is not the case with the REL. The full bandwidth signal is sent to the main speakers, and a "sampling" of the signal (via the 100K Ohm impedence of the sub) is sent to the REL to be low-pass filtered and amplified by the internal sub amp. The REL is then adjusted in terms of amplitude (volume) and crossover frequency to integrate with the natural low-end rolloff of the main speakers. The REL doesn't use another set of speaker cables (although you could make a Neutrik-terminated cable out of a speaker cable). A supplied cable is included with the sub (but you can find reasonably-priced aftermarket cables, too).