Man of Steel, Woman of Kleenex is more or less tongue-in-cheek. There's really absolutely no reason Superman's strength and invulnerability would prevent him from having a child, much less turn Lois into puree in the heat of passion. I can't believe I'm writing this sentence, but a Mr. Universe contestant wouldn't ejaculate any more forcefully than a 130 lb. weakling. And just like Superman doesn't tear his Clark Kent clothes while just walking around or trying to catch a cab, there's no reason to believe Superman can't stop himself from using all of his strength and humping her to death.
As for the genetic compatibility, the liger analogy is a good one, actually. The chimp and human, bee and human, cat and dog ones, though, are disingenuous. Kryptonians, although fantastically-evolved in some ways (not necessarily an evolution upwards-- it may very well be an evolution sideways... like the tiger and lion, again. Hell, probably not even THAT different), look 100% "human." I'd place bets on them being able to breed with Earthlings just on face value before it'd ever occur to me that they were completely genetically-incompatible. It's not like this is a question of a human being and a tentacled, green space-jellyfish. Being able to soak up the yellow rays of the sun might just be, on a genetic level, like carrying a gene for having red hair. No reason to assume it would hamper genetic compatiblity with a race of beings who, when you get down to basics and forego societal influences, look and feel and behave just like the same species.
I *****ing love nerdery.