Peter,
I read your post again and think the 2 from team A against 2 from team B scenario is still the most likely. So hopefully the following will be just what you are looking for:
Day1:
(A1 A5 B1 B5)
(A2 A6 B2 B6)
(A3 A7 B3 B7)
(A4 A8 B4 B8)
Day2:
(A4 A5 B3 B6)
(A3 A6 B4 B5)
(A2 A7 B1 B8)
(A1 A8 B2 B7)
Day3:
(A2 A5 B4 B7)
(A1 A6 B3 B8)
(A4 A7 B2 B5)
(A3 A8 B1 B6)
Day4:
(A3 A5 B2 B8)
(A4 A6 B1 B7)
(A1 A7 B4 B6)
(A2 A8 B3 B5)
Notice that if you sub-divide each team and make two ability groups (1-4) & (5-8), then every foursome contains a stronger and weaker player from every team.