Is it possible to use MD6 in C #?

In order not to be left unanswered, I will put here that it is possible, since every algorithm can be implemented in a programming language.

If you want to know if you have it in .Net. No, it does not. If it has in some external library. I do not know anything.

So you'll have to study it and make or ask someone else to do it.

But the question is: what for? Why do you want to use something that is not well accepted in the community?

You want a solution and this you get with other algorithms. Try out the algorithms available in the SHA2 collection. I doubt they will do what they need. One of them is the SHA512 that is heavy but very strong. In general, people even prefer to use something less strong and faster to calculate.

Example:

static string sha512(string password) {
    byte[] bytes = new SHA512Managed().ComputeHash(Encoding.UTF8.GetBytes(password), 0,
                        Encoding.UTF8.GetByteCount(password));
    var hash = new StringBuilder();
    foreach (var item in bytes) {
        hash.Append(item.ToString("x2"));
    }
    return hash.ToString();
}

See working on dotNetFiddle .