You will need ROOT and app called "DriveDroid"
Download Android File Manager - http://www.android.com/filetransfer/
Open DriveDroid app, give it root access and under its settings, change USB or Permanent USB mode to "Mass Storage Android Debugging"
Connect to OSX and open the Android File Manager app on OSX... next time you wont need to open it manually, it will open everytime you connect the phone.
This might break connection to HTC Sync though
(I use the above for my iMac)
Current Devices : HTC One, iPhone 5
Retired : HTC Diamond2, HTC HD2, HTC Sensation XE, HTC Sensation XL 16GB, Motorola Razr, Galaxy S2, Galaxy Note, Xperia S, Xperia V, HOX+, HTC Butterfly, Galaxy S4