Quote Originally Posted by samsc View Post
can you put up a grey scale and colour chart on each tv - at full intensity

then take a decent photograph of each screen

this will give you some idea of the gamma differences
To take Richard's method a bit further, I will actually point a Flat camera at each screen/TV and then use a scope to adjust the settings of the media server output. This has worked wonders on LED walls, different video projectors, and anything else which might pop up.