Beth,
Sorry I think I misread your e-mail. You want to post tracks you create? That also is a horse of a different color. First, don't post the Arlen for your own well being. It will be illegal though no one will likely come after you. People that post copyrighted pieces on the internet do so at their own peril, but the reality is that unless you are obviously making $ from it, the lawyers at most will usually just have youtube slap a commercial on it so someone gets some $. There are people and webbots that do nothing but search for copyright song infringements on the internet. But certainly we don't want to post copyrighted material on thereminworld.
I'm not sure that thereminworld.com has the ability to post .mp3 files. If they do and Jason is reading this I'd like to know how to do that myself.
But you can do this, which is how I distribute my music I wish to let others enjoy. (you could of course post it on youtube or create a public dropbox account too, etc). Go to www.imslp.org and create an account for yourself. You can then post stuff you write on your own composer page you create under common copyright. Or in the case of the Faure, you can go to the first link above which is the Pavan page and you can post the .mp3 arrangement you have made under the recordings tab (or synthesized/MIDI tab if you are wanting to post a MIDI file). Then you can just let us know what that link is and anyone here can go there to hear and use it. It may take a day for them to vett the file and make sure it not a copyright infringement.
Now when you post it on imslp.org you will be asked what kind of common copyright you want to use. Pick one that says non-commercial. This means people can use it, but not to try and make money from it. Of course you can say they can use it for any purpose including making money if you are so inclined. Note that imslp will reject anything they feel is either not in the Pubic Domain or is not written by the author posting it giving common copyright use permission.
Under common copyright you are giving up some rights but normally keeping others (primarily keeping the right to make $ from your works - or put another way restricting anyone from using your work for commercial gain). From there, you can choose to let someone edit or make arrangements of what you post - that is use it for any non-commercial purpose, or you can be more restrictive and say anyone can use it for non-commercial use but they can not make any changes to what you post. Or you also have the option to say - use it for any purpose you want including making $ from it (but I would shy away from that option).
Rich