I get asked this question a lot - why don't we have a generic file attachment/upload section like some other theremin websites?
The answer is unfortunately related to copyrights. Since I can't verify that every file uploaded doesn't violate a copyright or legal license, I'm not able to host such a service. Other sites have provided it, and they're running a high risk of being hit hard with a lawsuit. I don't have the resources to keep the sight alive if such a thing were to happen to us, so I choose not to run the risk. Some thereminists have even sold CDs with unlicensed performances of copyrighted songs - same thing. Unfortunately, this is why we don't use copyrighted songs for the contests either.
It's a shame it has to be this way, but until ThereminWorld is a massive media empire and can set its own rules, I'm stuck with it. I hope it doesn't impact your willing to participate in our theremin community & that you are able to find the site useful otherwise.