Sierra-2 X-over settings: FMOD 50 Hz, FMOD 70 Hz, Q-plug A or none?

[assassin]

Trying to plan a 2.1 system for music only. Using a Emotiva preamp/DAC which does not have subwoofer crossover capabilities.

What would you use to send only the lowest Hz to the sub? I will crossover the sub at about 60-80Hz.

Thanks in advance.