Set your receiver's crossover to 80 Hz, following THX recommendations, and then adjust the subwoofer level so that it blends ...

Use separate speaker wires for each set of terminals and connect them to the corresponding outputs on your amplifier. This method can provide a subtle improvement in audio clarity for certain setups.

[Adam Francis] bought some cheap speaker drivers from AliExpress. Are they any good? Difficult to tell without a set of enclosures for them, so he made a set of transmission line cabinets.