You are missing the point. The verses are Genesis one and two. In those two creation stories, we have a description first of God creating Man and Woman, but it does not say *how* He created them. Then in the second story, we have a description of a His creation of a specific man, and then a woman, and how He placed them in a garden. There are a number of ways to read this, as I have explained in the other Cain thread.
But which is the most likely? You say the YEC reading of single male and female from which every man and woman since has descended, and that He created none others. You say this ONLY because it is based on what you call a "plain reading" of the text. Yet, you are willing to follow a very "unplain" reading of the Cain story. Instead, you twist the Cain story around so that it fits with your reading of the creation of Man. And it IS a convoluted reading of the Cain story, there is no getting around that fact. You are reconciling the Cain story to your reading of Adam and Eve.
I am just considering (and considering is the key there) the same approach, but starting instead with the Cain story (for reasons I will give below), and interpreting the creation of Man story so that it is more consistent with a plain reading of the Cain story. The same process that you are following, but starting with a different section of Scripture and reconciling them, just as you have done.
Either way, you must read additional material into the text, since God did not provide us with a full and complete account (which was both uneccesary for His purposes and probably impossible anyway).
The difference is that the Creation of Man stories are more subject to various possibilities due to the fact that there are two of them, the poetic language used and uncertainty created by the original Hebrew. It is simply more open to interpretation than the Cain story. To me, it is much more certain from the text that there were others besides Adam and Eve's descendents living at the time of the murder.
So, you see that it is essential for you to be able to justify your "Cain married his sister" position in order to justify your reading of the creation of Man story.
The problem is that you state your position dogmatically, as if it is the only possible truth. I state my position tentatively, because I don't think we can discover the truth on this point and that taking dogmatic positions is not only arrogant, it is dangerous to the message of the Gospel.
Oh, and this has nothing to do with evolution. The fact that a few of the possibilities of how the others got here may somehow fit with what we know about evolution is besides the point. The others could have been addtional special creations either before or after Adam and Eve, which would not rely on evolution at all. The point is that there were very likely other people on Earth at the time who were not descendents of Adam and Eve and I am curious who they might have been.