For all the talk of sex these days amongst evangelicals, the Bible is really not very explicit nor exhaustive in its treatment of the subject. Its approach is not developed in detail from the ground up; but rather sex is treated as a given in human life, something assumed, and handled euphemistically with the less said the better. Generalities and principles are the best that can be inferred, and proscriptively, despite all the angst among the religious through the ages, there really isn't that much said at all. There is enough, however.
I can find but four absolute sexual proscriptions in the entirety of the Bible: homosexuality, bestiality, fornication, and adultery. The overarching principle, it seems to me, is have no sexual intercourse with any creature other than your human spouse of the opposite physical gender. There are specifics that fall under this principle such as no intercourse during menstruation or immediately after birth, and no incest (particularly cross-generational), but that's it, really. So much for the detailed lists that so many believers bandy about!
So how do so many Christians come up with so many proscriptions with so much detail? I think many rely on Natural Law. If one adopts the premise that sex is fundamentally reproductive in purpose, just about anything non-reproductive could be considered willful and ultimately sinful. Masturbation and birth-control are examples of such issues, though neither is ever mentioned in the Bible.
Other proscriptions are clearly man-made and cultural. Specific sexual practices or approaches to the act are most certainly never mentioned in scripture, but that hasn't stopped people authoritatively listing dos and don'ts that do not appear there. What I think can be said in light of what has been said is that whatever a husband and wife wish to do in regards to the subject is up to them. As long as they are agreeable it's nobody's business but theirs.
I wish the subject stayed that way. We are an oversexed culture! What ever happened to less is more? I think the relative biblical silence on the subject ought to tell us something in and of itself, especially today--we think too much and speak too much about sex. And that's just from the pulpit!