I, like you, am using a high crossover setting for the Motif center. Yesterday I connected my small subwoofer, an old Rel R218, to my Motif center speaker. It's connected only through the high level input. This is where it got interesting, and a bit frustrating. Rel states many times how to adjust the settings when doing this, but it doesn't work for a speaker that is rated for only 73Hz, it's just not low enough. Rel says to set the XO on the sub to its minimum, 30Hz, then increase the gain until it matches the speaker, then increase the XO till it's too much and back off a little. Again, it just doesn't work. Lots of low freq comes through but nothing even close to 73Hz, so there's a gap. Lucky for me I have REW, which made it simple. It ends up that the crossover on the sub is now set to 120Hz, and the gain is set very low where it blends perfectly with the Motif at around 100Hz, which is where the frequency drops like a rock on the Motif. So this is working very well, very happy. Also, I was not aware at how much very low frequency audio comes through the center channel. I always thought it was almost exclusively for voice, it's not. Lots of low bass, music, sounds - but not LFE. So having a dedicated sub for the Center is a really good thing, the audio seems clearer and more natural. I'm hoping to even out a plateau the Motif has when it's calibrated.