I don't think that Paul had any particular physical sex act in mind when he used marriage as an example of the relationship between Christ and the Church. I don't think that heterosexual genital coitus was in his mind, either. I think that Paul was referring to the overall intimacy involved in the entire act of human sexuality. It was the spiritual, emotional one-ness that he seems to have in mind.
The Bible seems to paint broad guidelines for human sexuality. Permissible sex is between a man and a woman who are married to one another as a private act involving no one else. Beyond that, the Bible is pretty silent on what sexual conduct is allowed in marriage. 1 Corinthians 7:1-6 tells us that married people cannot withhold sexual favors from the spouse. Verse 5 tells us the purpose of this sex is to deal with natural physical urges. While I might say ICK at some particular sex acts, it is hard to find specific chapter and verse to condemn them. If God hasn't specifically called it sin, then it is not my place to call it such - even if I might find it disgusting.
I think that sounds a little Manichean, arguing against the goodness and intentionality of our being created, male and female, in the image and likeness of God. Specifically as beings who are male-and-female, we express the image of God in our capacity to cooperate in procreating new human life. Jesus Himself specified about marriage that the two become one flesh, not spiritually and emotionally.
St. Paul also said, "Glorify God in your bodies." It's hard to square that with using your spouse up the **** because her natural makeup isn't good enough.