Glad to here about your successes with Solar Returns and progressions.
On the sixth, Ronia was right to interject other meanings, and the sixth has a link to slaves and servants. Now I know that most of us don't have slaves or servants as permanent fixtures in our lives but we might well have the next best thing.
John Frawley points out in one of his books that tradespeople we employ on a temporary basis will fall into this category - so you might find that you marry your plumber, electrician or satellite TV installation guy.
If you have a managerial post then you may well have subordinates and they too will fall into the category of 'servants', There's also a link to pets and small animals. Now some people do seem to 'marry' their dog/cat but I was thinking more in terms of someone who works with pets or small animals or who has a large collection of them.
Lastly there's a link to travel for all cadent houses, so the partner might be associated with travel.