Elevating subwoofer about two feet off the floor

Geoffkait unless your subwoofer weights over a ton the last thing you want to do is "mount it on springs." You will not isolate other equipment from it at all. Get a recording with test tones. Put on the 20 Hz track and turn it up. If your system will produce it at all the entire house will start shaking including the refrigerator and your wife. Low frequency sound waves are very powerful. You ever been around a sonic boom?
Subwoofers are best served locked down tight. There is an issue with the stiffness of the floor. Concrete is always best. 

Steakster you need to lower your dose of Adderall. I never implied anyone should not trust their own ears with their own systems. That does not mean I have to trust anyones ears with my own system. I will go where the science takes me long before I trust anyones hearing including my own. The people I help with their systems are not going anywhere near a Best Buy. I do so only by specific request and as a favor. I did work for Luskin's (RIP) when I was in medical school to help pay for tuition. It was a mid Fi store and a rat race. Far worse than Best Buy. That is the place they use to wire the speakers out of phase so the salesmen could sell the cheap crap they were being spiffed on. I always tried to sell the best equipment and failed miserably. The best equipment was always more expensive and people were more interested in cheap. If I work with anyone now it is generally money no object. What Fun!!
I am no where near money no object myself and never will be but I still get to build incredible systems in my dreams:) 

It is just a frequency response thing. If you had room control you could make the woofer sound the same and be more efficient and probably go even lower. If you have control of frequency response on the floor or in a corner is always going to be better. But if there is a response aberration and lifting the woofer helps and you have no other way of dealing with it you are stuck.