Where to use Isolation devices

I wouldn't call it an opinion but I always use three feet. It is stable and sounds better or the same as with four. One foot always goes under power supply or turntable motor if it is not totally separated. With cd player/transport or cassette deck I just move the feet under the component and listen.
I would see no reason to use only two feet and I doubt it would sound best.

Inna, when I purchased my Nordost Sort Kones I found it interesting that the Nordost website/white paper indicated that improvemetns could come from using a single Kone. They said that wine bottle corks could be used for the other two feet. This could be marketing hype to get people to at least purchase one or two of the Kones if three was too expensive, but it was an interesting concept. I can't see myself sitting my equipment on corks.

With your indulgence, a rant:
If I walk into a familiar room, full of knickknacks, I’m much more likely to notice a newly acquired knickknack, than I am to notice the removal of one. That’s because, over time, we all become consciously blind to details that are very familiar to us; or at least, we lose some awareness. Okay, where am I going with this? There is no element of audio that I find more agonizing than the struggle with isolation devices. Chief among woes, is that there is usually a give and take factor; and I notice what they add to the music long before I notice what was subtracted. Here’s the rub: since I can find no science to help me determine their proper usage - not to mention the outrages prices and snake-oil factor - I feel trapped. If I don’t use them, then what am I missing? And if I do use them, then what am I missing? Thank you for your indulgence.

The purchase and support of products that Claim to isolate should be a buyer beware alert. Isolation only exists in the absence of matter. Products that claim to isolate are a failure from the start based on such a premise that cannot deliver. At best these products merely re-tune your system to the flavor of the day. Mixing several of these non -isolation products together is the audible equivalent of trying to eat a soup sandwich. Resonant energy is still trapped and slow to leave it really needs to be provided a grounding pathway. Tom

Re-tuning or, better, correct tuning is perfectly fine with me. What is correct? Well, I trust my ears, the ears that actually listen.
One Kone and two corks? That's funny but why not if it sounds right? Somehow I doubt it though.