Hey all,
Also work in post production and am on a 2013 Mac Pro. Currently, I'm on Mavericks 10.9.4.
Ron, you are absolutely right. What Avid needs to do is release a new version of the DNxHD codec that is compatible with AVFoundation. When Avid takes care of this, QT X will no longer convert files, thumbnails and icons will work correctly, and the beloved Quick look functionality will be restored.
Navarro, be careful about RV64. RV64 and its various versions (RVIO, RV-SDI) do NOT support playback of DNxHD Quicktimes. The 32-bit version may still have support, but I'm not entirely sure. I have gone back and forth with Tweak software on this a bunch of times. I was particularly irritated about this because we bought a license of RVIO to do batch transcoding on the last show, only to discover that it would not work with the footage that was provided by editorial. According to Tweak, DNxHD is not an open source codec, and they were unable to negotiate a licensing agreement with Avid. I believe that since they are a commercial product, that they couldn't get away with reverse-engineering the codec like they have done with FFmpeg. This is not to say that RV is not an awesome product, which it is; just be careful with the codec support.
Hiero Player from the Foundry is a little cheaper than RV ($300-ish), and will play pretty much everything except Phantom Cine files. VLC is another open-source option as well.
-n