If you can hear a different between 20w and 22w, then your ears should be classified as scientific instruments. :p
You'll need to make a baffle using some 1/2" plywood or something. Just pop out one of the 6x8s and trace its outline onto the plywood. Cut it out and also cut out a corresponding mounting hole for the 4x6s. Presto! You've got baffles!
Different 6x9s take different modifications to be used in the 6x8 openings in Contiques. It depends on the mounting depth and speaker basket design. Some require cutting/grinding metal, some only require drilling new screw holes, and some won't fit at all. Try a search on 6x9s and see which models fit with the least modification.
