Glad you figured it out, Lirael!
Thanks for sharing your solution.
I have a Mac and 505 too. It is really inconvenient that with the 505 you have to authorize it on a PC. But, I suppose the 505 came out before Sony supported EPUB's and also before they had a Reader Library for Mac. Sony doesn't typically invest money in their older models. I think it's their incentive for people to upgrade to their newer ones. But, the 505 is so popular and was such a fantastic model that many people just don't want to part with it until it dies. That's why I still have mine even though I have the newer 950 now. Have a great weekend!