I have been facing the same problems…
I am on Mac Os X 10.6.5
I have dual display..
one is Eizo CG241w
one is Apple Cinema Display 23″
I use both Canon 5D and 7D for video footage.
I use Premiere CS5 to edit and then After Effects CS5 for color and compositing
render out as animation 100% quality and Adobe Media Encoder CS5 for different encoding.
and then to vimeo.
Please Check out my different output results with Match legacy option checked and unchecked.

If the match legacy option is checked before render, VLC is the only player able to display
as I see in after effects.
I did many tests with different codecs and same result, quicktime player is not able to
display correctly. So I am a bit confused what to trust. Since the default player that everybody
have on both operating systems is not VLC.
And all these problems occur when I get an output render from : Adobe Premiere CS5.
I am not using any color management because as far as I have tested my different color space
tests the color shift and gamma **** occurred as well..
Thanks for all the suggestions.
Koray Birand