Another thing you can try is Kies Air via WiFi. Enable Kies Air app on your S3, and then point your Mac based browser to the IP address that Kies Air on the S3 provides. You can browse internal and external SD cards from the main Kies Air browser session. Go down to the bottom left portion on your Kies Air browser session and you'll see the File Explorer option. Its worth a try as Kies Air does not require you to install any apps on your Mac.
One minor thing to look out for is browser dependencies. I primarily use Chrome, and lately have been getting a notification that "Java (TM) is required to display some elements on this page.". I open another tab that takes you to the page for "Install plug-in", and this loops into a message that Java 7 is not compatible with Chrome given Chrome for Mac is a 32-bit browser. For now I've been ignoring this problem.
You could try Safari, but I'm having issues with version 6.0.1 where it states "Safari can't open the page. "Kies Air IP string goes here". The error is: "The operation couldn't be completed. Operation not permitted" (NSPOSIXErrorDomain:1). I don't have the time or inclination to troubleshoot that further these days, but suspect that the issue can be resolved with a bit more research and/or workarounds.
11Oct12 Update: So I got tired of the "Operation not permitted" issue in Safari when trying to access the Kies Air session on the S3. A bit of Google sleuthing lead to a good thread on the Apple Support Communities
https://discussions.apple.com/thread/2296455?start=30&tstart=0
My particular firewall was blocking access to the Kies Air IP address and port combination. At first I tried granting trusted access for the particular IP, but didnt solve the issue. I reset the firewall config after exporting my current config. Not sure how a local LAN address became "untrusted" as I don't recall blocking it. So, no issues at this point with using a Safari based session for Kies Air access to the S3.