Do you use a Subwoofer when listening to stereo?

I thought using a 12 inch b&w asw 2000 sub would b good to allow my b&w 804 d3’s to better handle freq above 80 hz (ie. benefit from sharing burden).  I am not sure this is prudent as my well powered 804s can probably handle those lower frequencies just fine, and may make them sound better vs cutting them off from flowing thru the 804s.
My Stereo listening is done by streaming thru a nucleus connected via usb to a chord Hugo tt2 and then to a marantz 5014 via coaxial, then to a McIntosh mc255 and then off to speakers referred to above

 Does excluding sub from stereo make sense?
I use a sub (12" peerless XXLS subwoofer + KG5230 amp) occasionally when I listen to stereo. Certain music sounds good with little bit more bass added even though my full range speakers go pretty low. 

Yes on the sub/subs. Regarding the DBA, rooms vary and a DBA may not be practice for whatever reason. Only you can decide. But overall a sub system with stereo is excellent. Regarding your tv/stereo situation... simply run a digital (optical is good) out from your tv to your dac and out to your pre amp. HDMI sucks, and if that is the only reason you are using your Marantz is the HDMI hookup, you can do better. Ultimately, what do you want out of your system? The best possible stereo music playback, or TV audio? That will tell you what route to take...
A properly set up sub can give you increased clarity in the mid range, more detail in the bass, a larger soundstage and increased center focus. Wouldn’t be without one.