I make and sell orgonite which does not "block" EMF so much as it attenuates it. Some of my customers who place the "pucks" too near routers find that it can interfere with their wireless transmission, but it has never interfered with my audio system as far as I can tell.
Whether or not this makes any difference in audio I cannot say, but it definitely makes a difference for people who are electrosensitive, and I have over 2,000 sales of this stuff over the past 9 years. In a photo I have posted on this site about audio rack construction there is visible some of my orgonite pucks sitting atop a CD transport:
And this below is my website. This may look like shameless self promotion of a hobby business of mine, but it may be entertaining for the woo-haters here on Audiogon.