An EQ all the way because it serves multiple roles. It can shape speakers, act as a multi-zone control and much more.
The Throttle Box is a fixed notch filter and doesn't really do much for an XM9 specifically.
The XM9 built-in tweeter attenuation switch is a 1-ohm resistor on a 4-ohm tweeter so you get very little audible attenuation.

David