It might thump pretty good but your subs should blow it away. I'm sure it's producing some 40-ish hz bass, which is deep-ish bass but well within the audible range, and I guarantee it's not producing any sub frequencies with any authority. That's likely why it's not recommended. By the manufacturer that put it there and labeled it "LFE"...
. It might not fare well trying to reproduce true deep bass and can probably easily be overdriven.
I totally get hooking it up and playing around for sure, and I totally would myself just for shits n giggles. As far actually trying to integrate it with your dedicated subs tho it'll only hold them back.