You have a chicken and egg problem.

You don't seem to be a part of an artistic community.

The minimal design of your site is not appealing to artists and the lack of stuff to look at / download is not appealing for potential subscribers.

What is the value proposition?

You are asking a group of hackers on how to encourage artists to sign up to your site. This seems wrong.

Get out of the office with print-outs of various designs for your home page and get talking to the people who will make your site work, and gain some more perspective. Or, in short, learn about your customers.