Show audio file but require registration - suggestions for approach?
You could create a views block for the anonymous user.

1) add a content path field

2) Under Rewrite results, rewrite the content path field and use it's token. 

Ex: &lt;a href="/user/register?destination=[path]"&gt; &lt;img src="/images/playbutton.jpg"&gt;&lt;/a&gt; 

Note: (the ?destination= tag, will send them to that page after registration).

3) Change the view access from permission to role and select anonymous user.

4) Add a contextual filter of nid(node ID), select provide default value, select content ID from url. 

Then you could use panels, a block, or a view block, then just give it a role of authenticated and put your player there.