This same scenario has been happening to me for over a year with 10.6. When I select a Legacy Logic file like "Studio Upright Bass," Logic downloads the .exs file and then repeatedly downloads all the other audio files in my project. But when it is finished downloading I can NOT hear the Studio Upright Bass sound, even though the previous sound "Dark Upright Jazz Bass" played perfectly.
Please help help help! I've put off recording for way too long!