We actually do allow you to upload in wav, aiff, flac but you can only download in those formats if the tracks were uploaded in the same.

Using the WebAudio API we should be able to apply effects to the master bus. This is our first test of the concept and it expects that you will do most of the work in your DAW using the site for sharing. In future versions we want to add more in browser editing if we get enough requests for it. Thanks for all the suggestions!