First of all I am on PC and cannot help you. Second I want to bump your question so perhaps you can get help from a Mac user.
Last, I would say that I did not install the Sony software on my computer. It is just so simple to drag and drop book onto the 300 that I do not see the need to over complicate things with a DRM laden, billions of options and corporate designed piece of bloated software. If you really need software to put books on your Sony, then Calbre is a good free alternative solution. Calbre is also great for converting ebooks. Sorry if Calbre is not available for the Mac, I have not checked.
That being said, if you want to buy books from the Sony store (I don't) then I guess it is a good option. But there are many other options available. I do hope a Mac user chimes in soon to help you
