Mac does not play nice with MTP, which is the protocol used to transfer files back and forth between PC/Mac and Android.
If you are bone stock, just use HTC Sync and point it to your iTunes media folder in Finder.
If you are rooted and/or prefer ADB, download DriveDroid from the Play Store. Once downloaded, give it Super User permissions, then go to Settings > USB Settings > Manually Change Permanent USB Mode, then select Media Transfer Protocol. After that, go to your phone's Settings > Developer and enable USB Debugging.
Now, download Android File Transfer on your Mac. Plug your phone to your Mac and it'll load up and let you add/delete files at a whim.
With all that said... If you don't use ADB, HTC Sync will be the easiest and allow you to copy playlists from iTunes. With Android File Transfer, you can copy all the music, videos, whatever, but the actual playlists don't transfer over. If there is a way, I'd love to know.
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