I've had a Rythmik F12G for about three years. It's the best sub I've had in my house. Someday, I want to buy two of the Rythmik double 8" subs to pair with two-way monitors (assuming I don't decide to buy three-way floor standing speakers instead). I personally prefer the double 8" silhouette over the 12" F12G, but I'm told they sound pretty much the same.
Try to find someone near you who owns a Rythmik sub, or just jump in and buy one. Highly recommended!