If you're curious about his remark that death and sex are two sides of the same coin, you might find this interesting reading material: http://en.wikipedia.org/wiki/Death_drive
(and a translation of the source http://www.bartleby.com/276/4.html
). In a nutshell, Freud at some point of his career began to question his own "pleasure principle" (which basically states that all our actions are more or less designed to maximize our pleasure and avoid pain) since it wasn't apt to explain certain psychological phenomenas like masochism or repeated nightmares of war traumata.
The "death drive" (often falsely translated as the "death instinct"), he speculated, might be a subconscious tendency of all living beings to return to a pre-organic, lifeless and mindless existence.
I'm not an expert on the subject, so I better stop explaining before I say something wrong - you can read the rest in the linked article.
Freud's point is this: There is a death drive (which would later be associated with Thanatos, the greek god of the underworld), and there is a "life" drive to counteract it (associated with Eros, the god of sex).
Thus, what Kaufmann's trying to say isn't that sex equals death, but that sex and death together form a whole.