I have totally failed to get the theme. Hints welcome please for 7down.
The theme says solutions to 1, 2 and 6 are, perhaps apocryphally, 7 of a kind. None of the four is further defined.
7 is 'one having nooky with copper in river, all wearing glasses'
7,8
p is the second letter of the first word and x is the second letter of the second word.