Although there are places where a power conditioner would be advantageous, such as a large apartment building; I believe it falls in the gray questionable area. Think about it, we're improving the AC, not the DC which is where it makes a difference.
The manufactures of high end components have already spent a considerable amount in high quality parts, turning the AC into DC; I should think those parts would be able to withstand a blip every now and then; that's part of what you paid for.
Many reviewers have stated they prefer the amp straight into the wall.
However, if I spent a bundle on a power conditioner, I'm sure I would be able to hear the difference, kind of like the magnificent clothes the King was wearing.