Are you putting the Macbook into clamshell mode? When I hook up my Macbook to the TV, I load up the video player, then close the lid so it outputs only to the TV. I think if you have the lid open, it's using up processing power for both screens.
I have a black Macbook C2D 2.0 GHz and it runs various containers up to 720p (1080p - forget it) smoothly on my TV.
BTW, there's an update for MPlayerX v1.0.8 since Aug. 18th.
What's the difference between MPlayerX and MPlayer OSX Extended? Is one of them updated more frequently? (I notice that only MplayerX is available in the App Store).
Custom build of Movist with updated ffdshow. It sends DD and DTS signals to receiver. It crashes on first but on 2nd attempt, my receiver shows the DD and DTS symbols. It's subtitle rendering is the best I have ever seen. The subtitles can be pushed in to the black movie borders is huge bonus.
VLC on OSX Lion is useless POS.