Subwoofer with center channel

Sounds like you’ve got your priorities straight in terms of more highly valuing 2-channel. 😜  If possible I’d have all four subs working in a swarm array for stereo assuming you could have both LFE and L/R line-level inputs connected to the SVS sub simultaneously.  That’d be your biggest benefit in employing your NHT sub IMHO.  FWIW. 

@soix A speaker level connection with the SVS and NHT would be difficult.  I'm currently sending the LFE channel to the SVS via a REL wireless transmitter.  And, I don't really have a great spot for the NHT.  It would be interesting to try four subs, though.

It's a shame to not use the NHT.  It's a nice subwoofer.  I could swap it for the SVS, but the SVS is probably better for movies.  The NHT has two drivers in a sealed enclosure with an outboard controller.  I had NHT replace the capacitors and they also replaced the tracking voltage controls a couple of years ago.  They were very helpful and reasonable about costs.  I think I paid $150 for the repair..  

I run a subwoofer with my CC. Mid-bass or bass bin is a better description. I have thought about replacing my old Infinity Prelude Compositions; Mains - Model P-FR (2 ea.), and Center - P-CC, but they fit perfect in my small theater and still sound great and the foam surrounds are still as new.

The one deficiency was the center channel would only go down to 150Hz when running Audyssey on my Marantz AV7705. I had an unused Rane AC 22B crossover and an AuraSound NS10-513-4A in 1 cubic ft sealed enclosure I had built along with a spare amplifier channel and added it under my center channel to help fill the gap. I ran Audyssey with the bass bin added and the CC is now set at 80Hz and dialog and CC sound seems fuller and more natural. I have a TC Sounds LMS Ultra 5400 18" and 2 ea. LMS-R 15’s for actual subwoofer duty.