Interesting question, Aquarius7000! I don't have this aspect, but from interacting with a few people who do, I suggest that:
1. a partnership/marriage/committed relationship is very important to such people, yet the 7th is also the "house of open enemies." If the sun is in the 6th yet conjunct the DC, I think you would still find the person identifying with DC matters.
2. Speaking of Karen Hamaker-Zondag, I am a big fan of her book The House Connection, which is all about planetary rulers of the signs on house cusps. For anyone unfamiliar with this technique, she says, the house over which a planet rules serves the purposes of the house in which that planet stands. She works principally with modern rulers. So, for example, if someone has Aquarius on the DC, then the house placement of Uranus, as well as its aspects, say a lot about how that DC is going to operate.
3. I think people do identify very strongly with their AC--sometimes if they don't have a clear sense of identity [sun]--their AC can be very strong. [Here again, look for the location if its ruling planet, the "chart-ruler."] So suppose someone's DC ruler and the chart ruler are in a challenging aspect with one another--here you might see the "open enemies" dimension more than the "committed partner."
4. Consequently, the DC can indicate where someone gives away his/her power. In old-fashioned astrology, the sun in a woman's chart supposedly represented her father or husband. Consequently a woman with sun conjunct the DC might not want to be very autonomous, and might expect the man in her life to substitute for her own identity. Or it might show where someone blames somebody else, perhaps a very "solar" individual [the open enemy] for why his/her life hasn't worked out. [I am not saying you're at all this way, though, Aquarius7000--or others on this thread! Just very generally.] I think shadow material and psychological projection can be a real issue for the native.
But on the positive side, I would think that someone with sun conjunct the DC could make just a super best friend, business partner, spouse, tutor, mentor, psychologist, tennis partner, &c. because I would think they would be very committed to the success of a good one-on-one relationship.
5. Re: "withdrawing into a shell." I just don't know--I would have to defer here to Hamaker-Zondag. I do think this tends to happen when someone has Cancer rising.
A really good book on the dynamics of both the AC and DC is Jodie Forrest, The Ascendant.