Using a Rel Sub with a dedicated center channel

Anyone using a Rel subwoofer with their dedicated center channel in a home theater? Rel has a video on their youtube page from a couple years ago on how to do this and talk about the benefits a little. Someone in the comments makes the case that any channel in a HT can benefit from a subwoofer being added but it does have me intrigued. So much of the sound comes for a HT comes from the center channel it makes me think it might benefit. I am already running 2 SVS SB4000 in my setup. The Yamaha CX-A5200 I am using sets my B&W HTM 1 center channel at 120 hz for crossover and the Vandersteen 2ce sigs that are my are RL channels to 80hz. I actually really like the sound of everything right now but think maybe this can take it to the next level?
Could the sub potentially fill in the 60-120 hz range for the center channel though?

You mean like your two existing subs are now??

I'm not sure you understand how this works in HT. The HT processor is already sending this to your existing subs. You aren't losing anything.
The B&W HTM 1 should have no problem going down to 50-60 hz.  I would set the center to LARGE in your situation and just live with that.  It's gong to be much better for male vocal and other things.
I just looked at the specs, after @auxinput commented.

I’m not sure large is the right answer, but 120 Hz seems like a very high cut off. 80 Hz is the THX standard, and a better compromise.
The problem with setting them to large is potentially more distortion, so my recommendation might be to try these two options. Try setting to 80, and then to large.

Remember that in either case, your HT processor should send the remaining bass to the other two subs. 
I’ll try setting it to 80 hz first and see what happens. I have been planning on getting a better amplifier to power my center channel. I’ve got a Marantz mm8807 for the center and surrounds for now. I’m sure it’s plenty good for the surrounds but B&W usually like lots of power. The Yamaha sets the freq to 120 hz when I do it’s ypao corrections. I was worried about setting it lower than the 120 as I’ve read you generally shouldn’t go lower?