Hi Wiel,
I fully understand your frustration on this.
Open with Explorer is achieved via WebDav. Mac OS X requires Basic Authentication to be enabled on the site to manage files and folders. However this setting could not be changed because of security risks.
The Sync button is used to launch local SkyDrive Pro or SharePoint Workspace application. These applications are used to synchronize current library. It can only be used on a Windows device. SkyDrive Pro and Workspace applications have not been supported with Mac OS X. Although users can use Document Connection to sync with SharePoint libraries, I’ m sorry this is also not perfect. At least it cannot meet your downloading folders requirement.
Office 365 should be a multi-platforms product. Currently, Mac OS X has not been seamlessly supported like Windows. However, I believe it will become more and more compatible in the future. SkyDrive for Live services has been existing. I think SkyDrive Pro will also be available. You may also end feedback to our product team via the following link.
http://g.microsoftonline.com/0BX11EN/135
The new feature releases often originate from customer’s feedback. In the feedback description, please specify your situation and requirement in detail. Hope SkyDrive Pro for Mac will be available in the future so that your requirement can be met. Thanks for your understanding.
I apologize for any inconvenience this may cause.
Best Regards,
Kevin Cui