Center Channel and Subwoofer

I currently have a KEF T301C mounted below my TV, and 4 ceiling speakers (two fronts and two surrounds). All of this including the HDMI is hardwired to an X2800 in a closet. I recently purchased the home from the original owner who had it wired this way, so running additional wires would be rather difficult. I need recommendations on a better center channel as well as a subwoofer, preferably one that I don’t have to run an RCA cable to (if it needs to be done then I can figure out a way). I appreciate any help.