You need some sort of search function right on the front page.
I agree using YouTube for sharing music is a bit overkill, but it's nice to be able to just get to YouTube, search for some obscure band, and find random tracks immediately.
By not focusing around search you're forcing your users towards functionality in which they personally upload tracks to send to their friends. I find myself less wanting to upload tracks to share, but rather wanting to share links of stuff that already exists in the system with my friends.
Make that piece of functionality prominent and you're letting visitors easily leverage the work of the people that actually want to be a part of the system, as most users probably just want to be casual users.