What do you have the crossover set at on the sub itself? I think with KLF-30's you're looking at it being crossed over at about 60hz.
If it is crossed over right.....and is phased right.....and is in the proper location you shouldn't even know there is a sub in the room. The sub is going to compliment everything the speaker already does with an emphasis on the deep lows. It will enhance the mid-bass but that's it. That may or may not be enough for you. A good sub should make your speakers sound as if they have more "body" to them. Remember, you're listening to the speakers not the sub.
If the 30's still aren't kicking out enough mid-bass for you, you might want to check something like the JTR Growlers.
http://www.jtrspeakers.com/growler.html