I love this thread. Every time I come here I end up chopping and changing it.

Shin's theme: See what I've Become

Shin's battle theme: The Battle is to the Strong

Shin's Hakai form theme: Master of Puppets, S&M version (skip to 1:08)

Master of Puppets is true to his nature and I can't think of a more powerful song for his most powerful form.