I haven't read a post where someone has done this, so I'm wondering how it would work. I currently have a pci 20-39 in a 18x23x8 room with no openings. I love the bass I am getting, but after a year of getting used to it I want more. I want to buy a sub that will satisfy me without ever wanting for more bass and I want to spend less than 1000 dollars (the less spent the better however). I thought about just pairing my sub with another pci, but like I said I never want to upgrade again and what if that's not enough? I am thinking that if I get a plus than I could make sure that the subs weren't cancelling each other since the plus has the variable phase and it's also tempting because of the better woofer. So, would it be ok to have the two different subs running together? How much db gain would I get if I get a plus? (it's gonna be awhile, I still need to buy a center and rears to match my new axiom m60's but I can't help thinking down the road).