Gallo Ref3 - 2nd voice coil

I'm still learning, so please excuse me if this is a silly question.

I have the Denon 3805 which has multi-zone amp capabilities. If I'm only running 5.1 (of the 7.1 available), can I set the extra unused amps to bi-amp the second voice coil? If so, would I need to use a low-pass filter, like F-Mod?

For more info on the refered technique, please see link below.

I don't know why you couldn't use the other 2 channels, but I THINK you'd need to drive the active crossover/low-pass filter with full-range signals. You'd then send the low-frequency signals to the poweramp-inputs. The LP-filter would have the necessary level and perhaps equalization controls, too.

So, for the price of 2 pairs of interconnect cables, 1 pair of speaker cables, and 1 active low-pass filter, you have the equivalent of the Gallo bass amp/filter.
You must use a cross over to run the second voice coil, to augment the bass where the natural roll-off occurs (around 40hz). I'm using an Outlaw Audio ICBM, but you can use any low-pass filter.