I'll be backing David's statement.
From what I have seen, Promotion Forums are purely only for some genres, and those ones only. Everyone I see who only promotes on a promotion forum either runs an Admin forum, a General Discussion forum, a Gaming forum, or some other promotion forum. That's the only things I see from there. Someone like me, who owns a very specific genre, can't rely on post exchanges because those people might not know Rock Band, and that's absolutely fine. Not everyone plays Rock Band. When I do a post exchange, I end up getting 95% off-topic exchanges because they don't take the time to learn the specific genre. On some other forums, I will get people who will do that in a post exchange, and I commend them.
For someone like me, I have to rely on RockBand.com, ScoreHero, Google, and social media to get members in.