Some of this was summarized in a previous answer here. There are many opinions about this stuff, by the way.
Rabbi Yehuda Herzl Henkin's Bnei Banim 4:16 is a MUST READ.
It addresses the halachic angle on some of these matters, while Rabbi Aharon Lichtenstein's "Of Marriage: Relationship and Relations" (Tradition 39:2) addresses the "hashkafic" (philosophical) angle.
Here's some vitally important material that the Steipler Rav wrote for chassanim.
Yocheved Debow's book for parents is also important. (Especially as chosson teachers may find themselves answering questions that parents never did.)
In short, some of this was left as oral law. You'll notice that the language is different even within the Shulchan Aruch between OC240 ("how to be a very holy person") and EH25 ("how to treat your wife.") Rabbi Henkin's essay goes through some of the frustrations in trying to determine what laws on this subject were codified how and where. There are contemporary opinions that run the gamut from "everything in EH25 is absolute halacha, plus a bunch more things are assur too" to "these reflect a certain set of minhagim that may be recommended in some situations, and occasionally an ascetic philosophy that is not the right one for our time."
Personally? I recommend chasanim not read OC240. We decry how damaging inappropriate videos are to marital relationships because their focus is "whatever makes me feel good, I don't have to think of the woman as a person with her own feelings, wants, and needs"; as the Steipler letter points out, some of the ascetic material in our rabbinic literature (which as Rabbi Lichtenstein points out, leaves us perplexed where it came from) seems to say: "just do whatever gives you least pleasure so you can be holy", ignoring that there's another human being in the room with their own feelings, wants, and needs. A martyrdom attitude -- "I will try to totally ignore my wants whatsoever and only do what I think is good for the other person" -- tends not to work in normal relationships either. This has to be about two people who respect each other and work together.