Mike Hodges reports about EMPUSA for Fangoria online:
http://fangoria.com/news_article.php?id=4883
Hodges' article covers the dismissal of original director, Carlos Aured, Naschy's disappointment over this and his stepping in to finish the project. (Apparently, Aured's contributions have been jettisoned in large part, if not totally, so the film is Naschy's own.) Though Naschy admits that the project was "one of the hardest and most unpleasant shoots I’ve ever experienced,” he is "very grateful to everybody for the way they all knuckled down and for their wholehearted commitment once the initial problems were sorted out, and I’m pleased with the final result.”
Much more at the above link.