So the low driver in that speaker, the powered ones, needs an RCA input? What frequency does that operate? Does it have its own crossover control?
Or, speaker input to the whole speaker and that also feeds the powered driver?
No, the "LFE" or Low-Level Input does NOT need RCA Input, but it is an option.
Basically, the speaker will SUM all the BASS from all the sources. There is one crossover for the speaker.
You could just use the regular speaker wire and set the speaker type to LARGE/FULL RANGE + Subwoofer. The crossover will then send the low frequencies to the subwoofer driver and the other frequencies to the midrange & tweeter.
If you hook up both the RCA LFE + Speaker wires, the subwoofer will be active every time it gets any LFE signal from any channel. For example, if the LFE is from the Center or Surrounds, the powered subwoofer in the front Left + Right will also get the action.
If you hook up just the speaker wires, the powered sub may only get the action if the LFE is from the front Left + Right.
So potentially you get more bass if you hook up both the RCA LFE + speaker wire.
I don't do this right now because I already have enough bass from just the speaker wire in my current room. But when I move to a bigger room and have five BP7000SCs, I plan on hooking up both the RCA LFE Inputs + Speaker wires.