Somebody is infriging on my friend's rights by selling his audio meditation. How to deal with it?

Your friend is probably saving himself a whole lot of grief in not pursuing a claim.

If the publisher is on different continent, it would be very difficult to pursue and even then, it may not be worth pursuing unless there the alleged plagarized tape is very popular and generating a lot of income and the publisher has significant assets.

One solution to do something without letting it just pass, would be for your friend to contact the publisher of the company via certified mail with a return receipt and indicate that he feels his work has been plagiarized. As your friend has put it out on his site for free now, a good solution to request may be for him to indicate all he wants to settle the matter is credit for the song and/or that the net proceeds from the tapes be donated to a worldwide charitable association, such as the Red Cross.

As the publisher would have the same obstacles as your friend in trying to pursue a lawsuit, and your friend has it on his website for free and it is not generating any income, it is highly unlikely they would pursue the matter. To err on the side of caution, he should keep copies of any records that demonstrate that he distributed this tapes several years ago and possibly get notarized Affidavits of a people who can acknowledge (just their statements typed up and witnessed by a Notary Public - all banks have them and if or the person who signs the document has an account there, the Notary usually does it for free) the same and keep it them in a Safe Deposit box.

First of all, did K copyright his material?

If not, then there is nothing he can do. Even if he just declared it was copyrighted, without registering it, that is something that can protect him, but harder to prove in court than a registered copyright.

He should at the very least, send the guy a registered letter stating that the material is originally K's and that the other guy should stop selling it. A registered letter or whatever kind of letter that will verify that the other guy received it. That will establish that he challenged the sale of his material should he decide to take action later..