views and contextual filters with entity reference field
In the contextual filter, you can use php to supply the argument.  There, you could put in something like:

$node=menu_get_object();
return $node-&gt;field_headliner[0]['nid'];


where field_headliner is the node reference field of your event content type.  The exact syntax above is D6, but I am pretty sure it's the same or at least very similar in D7.

Then, just as long as this view block is being show in/on an event page, the above will return the nid of the headlining band, and if your view is set up to filter on that node nid, you should be set.

You could even get fancy up in there with something like:

$node=menu_get_object();

switch ($node-&gt;type) {
  case 'band':
    return $node-&gt;nid;
  case 'event':
    return $node-&gt;field_headliner[0]['nid'];
  default:
    return 0; // or however you want to return an error
}


and then the same view block display could be used on both types of page.  Then just put this block on band and event pages and you should be all set.