Anyone replace the springs of a Nobsound footer?


I purchased two pairs of Nobsound spring footers to place under my REL S/812 subs.  The front of the sub is much heavier than the rear of the sub, so the two Nobsound footers under the front of the sub, with all seven springs installed, are compressed nearly 90%-95% (rather than the 50% that I understand is optimal).  I’d like to purchase some stiffer springs to see if this will work better.  
Have you purchased any other springs that were different in stiffness than the springs that come with the footers?  If so, where did you find them?

in advance, thanks!

louisl

Why not just buy another set and use more under the sub. Or just use the feet on the sub as they were intended and don’t waste money on these tweaks. I never cared for these anywhere in my system. 

Might be easier to just put 2 nobosounds under each corner.  I'm a physicist and have worked a lot with spring constants and it is hard to figure out what springs to buy without buying a lot and trying them.