My experience adding subwoofers to 2 channel

My Kappa 9 speakers are rated to 29hz and they sound pretty good in my 18x24 room...powered by McIntosh mc1.25 amps...l was looking for another layer of bass to enhance the first experiment l took my SVS pb16 ultras from my theater room and tried them sounded terrible,didn't blend well..couldn't hear a difference until you turned in up then it rattled the room final experiment worked..l used 4 Velodyne minivee subwoofers(1000 watt rms class D sealed 8 in.) and after hours of calibration l hit it......lve got the bass response that exeeded my expectations. ....l should have done this along time ago....can anybody tell me of another subwoofer that may work even better?
After reading the threads here and doing further research,I added a second sub last week.I was so pleased with the improvement I've got two more  on the way to complete my 'swarm '.
My subs are located behind my main speakers in the front corners...behind some silk cant see them ...makes it very "steathy"and cool......l will try all four corners McIntosh C52 pre amp has switchable outputs for tri-amping so l can turn the subs on in groups of two or turn them off from the preamp front panel...very convenient. ....the "swarm configuration " will be the next phase ......the receptacles and audio cables are going to take some planning. ...thanks guys for the cool advise! 
Its amazing when it comes to bass how much better more is than few. With subs unlike the L/R stereo pair the subs can be completely different and located almost at random and yet still work just fine. So they can be "cobbled together" buying whatever you can whenever you can add and still wind up with excellent results. This might even be the best way to go, because of all the flexibility being able to adjust crossover and level of each individual sub. If you can afford a better sub great, but if you can only afford a cheaper one that's great too because more is always better.
Well Vin, you've gone and done it. Could it be that you filtered through all the pontification of endless subwoofer suggestions and found you're own suitable success? It certainly sounds that way!

I'll apologize in advance for one last thought. If you find yourself beginning to differentiate between your mains and the subs then I suggest considering Eric's advise.

Keep your eyes peeled for a small used Velodyne DD Plus. You can slave all the Minivees off the DD. The Velodyne Room Optimization program goes much further than Anthem, JL Audio, and even Magico. What took you hours can be accomplished in minutes. You'll gain remote control, volume, six presets of customizable alternative settings for when you go from Paganini to Prince, maybe even one for the SVS.
Just a thought, and again I apologize.

Enjoy the deep end.   
I totally understand the trick adding subs is you shouldn't be able to differentiate between the mains and subs....they sould seamlessly blend and disappear. ......when l activate mine ...the best way to describe it is like a loudness button on steroids. fellow Audiogoner said he went to a high end shop and was demoed a Rel sub to add to his system. ..he said he couldn't hear much of a difference and thought it was a waste of money. ...l belive source material is key...but everything sounds better with properly done subs......