Originally Posted by ahmedreda
Any help would be appreciated..
Start over. Don't throw good money after what you've already spent. Instead, upgrade to current ID, 15" subwoofers such as what you will find in the Rythmik, SVS and PSA offerings.
It's an imperfect world. Yes, it's not the cheapest avenue. Yes, it throws your idea in a tailspin. With that in mind, starting out with two Rythmik, LV12Rs with an eye on additions, six months or a year down the road, in my opinion, would be a more fruitful path.
When it becomes time to upgrade, that's the best time to trash what you have happening and start over.
In your case, based on available budget, purchase a single PSA, XV15, integrate it into your system and later add additional XV15s.
(ignore any factual integration complications as rest assured, by adding additional XV15s to your system, and taking old Pro 600s out of the system, automatically, everything will balance out)