Best sub isolation?

Springs are the best solution, for sure. The method mitch2 describes will certainly work. It is however a lot of work. I went through it and have some springs. You are welcome to them. For about what it will cost just to ship them you could get a set of Nobsound springs. These work just as well but a lot better because you don’t have to calculate anything just add or subtract springs as needed. The leftover springs can be used under other components. Easily the best value in bargain vibration control.

If you want a lot better Townshend Pods or Brackets are a lot more money but worth it. If what you really want is isolation then Nobsound. If you also want improved sound quality and are willing to pay for it then Townshend.

In between, the other stuff you are considering, costs a lot more but not any better than Nobsound. Only worth paying more if making the jump to Pods.

Good call on the Nobsound springs, definitely easier to implement and more versatile.
Setting up individual springs may take a bit of trial and error.

Townshend, but for that sub, I think Nobsound would do just fine. I would try 4 springs to start with, but since the sub is not that heavy, 3 per foot might be fine. I had to put 3 tiny drops of superglue beneath the rubber pads that go under the feet of my subs to keep the pads from migrating.

I had the Iso200 and $24 springs are much better.

boing, Boing, BOING! 24-29.00 usd.. Works great..

Regards