thanks for the excellent analysis of the instictual dynamics in relationships. I am a sx/so 5 (strong 3 and 8 components, strong second variant) and had some longer relationships with sp/sx women. It's absolutely true that they have the potential to soothe my dominant sx instinct and that there is sort of a mutual understanding due to the same energy direction. However, my personal experience is that this kind of compatibility is not a good basis for a lifetime relationship which includes family, kids and all that. The more the relationship moved from mere romantic encounter to making a living together, the different variants became a problem. It was always about priorities of both individuals that are just difficult to handle. The mutual understanding was not "bulletproof" in stressful everyday situations. Things like that show up when there is not much time left for togetherness. The desires were just too different. While this may be just a personal thing I feel that there is one real flaw in matching sx/so with sp/sx. The sx first partner enjoys this soothing effect. But what about the sp first partner? Reflecting my past relationships I feel that it must have been awful on the long run for my partners not to be understood in that soothing way. I mean, I am in good contact with my sp side and many people would perceive me als "self-preserving". But the first instinct is not only about that but rather about a symbolism around the themes of the respective variant. While I lead a successful and solid "self-preservational" life I am certainly lacking that kind of symbolism, giving an sp first person the right signals from time to time that I care about their personal wellbeing, security and so on. Living closely together with sp/sx partners was always like I couldn't do it right for them. And with their highly functional and balanced sx instinct they knew how to screw me up by withholding the certain kind of energy and symbolism I need. In times with less stress and more time we could bring that in balance again. I developed some empathy for the sp first insecurities... But this kind of re-arranging somehow felt like "why is that necessary, couldn't it just be naturally easy?". In fact, I would have been willing to do that "work". But what was even more difficult and really frustrating for me in the end was the lack of understanding for the so interest by my sp/sx partners. This was in the end really limiting. My natural flow of life as a sx/so is to reach out to people, make connections, be part of group dynamics, associations, having a fascination for might and power, connect to influential people in a group, become influential - and all that in an easy flow not as compulsive and nervous as among so first people. None of these desires were understood, not even a little bit. The dynamics was always like: If you care for such unimportant things, it means that you don't care for our wellbeing. For me this was a really hurtful signal, leading me to reply like "the connected society is part of the wellfare we both live in and would not be there if all people just cared for themselves in a secluded life".
To make my long story short: After all I found that the perfect relationship match is just the same instinctual stacking. My wive is also sx/so (so not as strong as in my stacking) and we seem to manage all things in life just easily without having to re-arrange. No conflict we had in many years ever got to the deep level of instinctual frustration. It's more like: How can we arrange our interests in a way that works for both. The really great thing is that the priorities are never in question and no one ever becomes abusive to the desires of the first instinct - because each one knows how hurtful it can be.
(I realize that the second instinct always has the potential to control people with the respective first instinct. I somehow know how to wrap so firsts around the finger and stay much cooler if the situation becomes difficult, just because I am not that needy regarding the maintenance of the status. On the long run I felt controlled by sx seconds in a similar way.)
In the end I think it depends on the life situation. I wouldn't want to miss the experience with sp/sx and it gave me the basis to get cooler with my first instinct. But it was really not the basis for eternity.