Thanks for posting on our Community, @lookere!
If you have the desktop app installed on your computer, and all of your files are synced to your device’s local Dropbox folder, you should be able to upload them directly to SoundCloud, for example, without downloading them from the Dropbox website first.
You can just select the option to upload a file to SoundCloud and then, pick the one you want from your File Explorer/Finder > Dropbox folder.
I hope this clarifies things, but I’m here if you need something else.