[Electrodynamic]

You can use a sealed enclosure, but a ported enclosure will perform much better. If you do go sealed, the 3 ft^3 sealed enclosure is a good enclosure volume. As far as power goes, put as much power on it as possible.

I wouldn't run two different subwoofers because you'll end up with two different sounding subwoofers playing at the same time. You'll also have two different F3's, so one sub will loose output while the other sub is still playing. Think of it as having a Dynaudio right channel speaker and a Focal left channel speaker.