8in is more of a mid-woofer than a subwoofer. Is this for movies or music? What type of music do you listen to? Or what percentage of each? What is your budget?
I have a Rythmik L12 in our 1400 cu ft master bedroom but I would prefer two someday but my GF will not go for that.

I think if I could do it over again, I would have done a L22 there due to the small floor footprint since only one box is her preference over 2 for some strange reason.... If not for WAF, definitely two L12s was my original scheme.... Maybe I’ll just stack 2 L12s and see what she does. LOL.

In the man cave / theater room I’m doing dual Rythmik LVX12 subs. I only bought one so far though. It is super loud and the only reason for two would be for perfect bass all throughout the room. The output from just one is already perfect in 2600 cu ft

If you are on a budget, I see used subs on Craigslist from SVS and HSU regularly. Good luck!
