It's been... I don't know how long, and the doujin section is not getting anything new. I suggest that put the Doujin section's links in the main page of the site to increase its visibility.
I imagine that you are planning to not put it in the main page until it has grown enough (or at least until it has one song under each letter..), but that simply won't work. If people don't see it, they won't submit anything to it. It will just stay empty.
Just put the links (even if the page is half-empty). When new visitors see that there's a Doujin section and it's still new, they might think about submitting anything they have.
This won't be as slow as you think. Doujin music sales are 48% of the music sales in Japan.
If it helps, I'll make a poll to see how many people agree with me. I might be wrong after all, but if there're too much people who agree on this, I tihnk you should consider it very soon. It'll help the growth of the site.