Yes, it needs a single input, not a stereo pair, though this is true for many (most?) of their models. It sounds like you want the sub to do full crossover duties - inputs and outputs. If so, you'll have to look at the amps of the various subs to find this feature. One example could be the F12 with an A370PEQ amp, NOT the standard A370PEQ3.

From their web site:
"The standard amplifier is A370PEQ3 (370WRMS PEQ). The quickguide of the A370PEQ3 amplifier for sealed subs can be found here [bad link]. A370PEQ3 amps do not have high pass filter RCA outputs. But it does have dedicated LFE inputs allowing for easy integration of a 2-ch-plus-HT system setup. A370PEQ amplifiers are available for those who still need high pass filter (or HPF) RCA outputs."

Check with Ascend or Rythmik for detailed confirmations.