There are a couple interesting options in which I would replace the front stage and move the NHTs back to allow for 7.1.
First, I have access to a pair of JBL 4410. Though they're only 90db, it seems like they might play louder than the NHT if fed enough power (I have an Ashly PA amp lying around). This would be the lowest cost option. Second, the Behringer B215XL has some fans...I don't love this option aesthetically but could make it work.
That said, I cannot accommodate either as a center. Would it be advisable to do one of those two as L/R, purchase a new more efficient center (Paradigm 500c, PSA, Triad)? Would either give me a little more volume and still provide acceptable sound?
I don't have a set budget for this, but if the answer is replace the entire front stage with PSA or above, I'd likely accept the limitations of my current system and move on.
Any insight is appreciate. Thank you.