Brandon,
Developing legitimate communities is, as I'm sure you're aware, one of the hardest things to do, regardless of whether that community is in the real world or online. The most effective traditional ways of building community all center around one very simple axiom of human psychology; human beings do not like to change their behavior without an overwhelming incentive to do so. One of the hardest behaviors to change are ones that revolve around social networks. How do you get someone to change their set of friends or people they relate to? In most cases, you don't.
What value does your forum provide to the user's life or online experience that any other forum dealing with the same field do not provide? Perhaps one way to approach this issue would be to identify what aspects of music forums you dislike and then figure out a way to ensure that your forum avoids those pitfalls. It's very likely that if you have negative feelings about a specific aspect of music forums, there are many others that feel the same way.
Rather than trying to push and prod people into your forum, allowing them the opportunity to co-exist in a place that avoids all of the trappings of the generic forum might create a sort of win-win vacuum. Once you hit a specific tipping point of members, your only issues will be how to deal with the onslaught of new members, but that is an entirely different issue altogether.
I hope that was helpful and good luck.
I feel that simple is better. Also, have you ever liked one forum better than another just because of the look of it? Seriously, a flashy looking forum never attracted me for some reason.
