In my experience (just me moving stuff around, changing settings 100,000 times) more subs are better even if they don't match. At the moment I have a 12",10" and 8" sitting where each sounds its best. Sort of a staggered triage in my room. I'd add the fourth (second 10") but I can't find a way to get it here for a reasonable cost. Of course having identical subs would be ideal but isn't always an option.