Subwoofer with center channel

I think we may be confusing/conflating two different issues in this thread. I read the original question as applying to a center speaker with an integral subwoofer, not a separate sub altogether. I have four different AV systems, and one of those uses a Definitive Technology CLR 2003 center speaker, which has a built-in subwoofer. Set correctly, it does not induce any  boominess or chestiness into male vocals. It does make a big difference on things like explosions/gunfire, giving much greater impact in the center channel. Of course, I also run subwoofers (at least two) in each of the AV systems.

@discnik That is the how I interpreted it. A subwoofer, used as a mid-bass in my example, functions just like a speaker with a built-in subwoofer, it just uses an external active crossover. If the OP wants to continue using the center channel they like except for bass extension, adding a bass bin via an external crossover that only addresses the center channel signal is a potential solution and the one I use. I use a high pass of 80 Hz and I'm not sure but around a 150 or 160 Hz low pass between the bass bin and center channel. This is right in the sweet spot for the AuraSound NS10-513-4A in 1 cubic ft sealed enclosure.

Late to the thread, but I’ve been using a sub with my center channel speakers.  I have a REL S/5 SHO and a pair of YG Acoustics Carmel 2 speakers as the center.  The center channel is set as full range speakers from my pre-pro.  Regarding the amplification, I use an RCA cable to a Y-cable single RCA female in to 2 males out to the left and right channels of my amp.  The result is seamless integration with my mains which are YG Hailey 3’s and a pair of REL No. 31 subs.