I tried every combination of usability settings and could not get the Control Panel to show up for the Feedback Moderator users. They do have Edit Module permission on the Feedback module by the way. On a whim, I gave them Edit Module permission on the corresponding Comments View module on the same page, and -- presto! Control Panel. So, evidently the Control Panel visibility is based on the Edit Module setting of the Comments View module, not on the setting of the Feedback module. Anyway, it's working now but I wanted to share this solution in case anyone else runs into this. I appreciate all your help, both of you.