Well, I have to say that I am still only engaged, sorry that I wasn’t clearer about that, but I have thought a lot about this topic to try and get a better understanding of it. Honestly, I think a lot of it is semantics, though I do think there is a deeper meaning to it as well, which I am still trying to grasp more fully. At the very least, there is the fact that the sacrament of marriage is supposed to be a sign of the relation between Christ and his Church. I am trying to find where Casti Conubii talks about this and, again, will post it when I do. So, especially if the way it plays out in marriage is pretty much identical in exterior actions etc it seems that this way of thinking about it is better because it helps keep one more in touch with the great mystery of the union of Christ and His Church, of which it is a sign. On top of that, as I’ve thought about it more, I’ve realized that, at least for me, thinking about the equality of the relationship rather than the head/heart relationship tends to make me think in a more selfish way rather than to think and act selflessly for my (for now) fiance. When I’m concerned with insisting that we have an equal relationship (and yes, I’ve been there

) I find that I am worrying more about ensuring that
I get as much as
I deserve. When I think of it in terms of head/heart (both of us serving each other out of love etc) it turns more into a matter of worrying about the other. Maybe thats not a universal experience, but I think that it can make a difference. I would say even if you focused on the mutual submission part of that passage you would be more inclined to focus on thinking of the other rather than oneself.
I know I’m kind of just rambling here, I’m still trying to understand this better myself, which is why I suggested people take the time to prayerfully and openly read casti conubii to try and come to a better understanding themselves of what it is saying. It is definitely not just a simple clear-cut document, like most encyclicals/church teachingss there is so much depth beneath the surface that you have to dig through to get at.
In a head/heart relationship as I understand it
both people will give in to the other and submit to other, I think that thinking about it as head/heart gives a different attitude to both the husband and the wife, not just in being other centered etc, but even in the way they approach their submission to each other. Its not so much that the husband will get his way more often in a head/heart combination, or even that the woman always has to obey her husband, but that when the each submits to the other their way of doing so and motivation for doing so will be altered very sslightly to help better echo the relationship between Christ and His Church. Again, I know I’m kind of just rambling, so let me know if this is just too confusing, and I can try and clarify what I mean. Trying to understand this is a work in progress, but so far this is where I’m at.