Is the output from the DVD RGB or component (Y/Cr/Cb)? RGB isn't "self contained" as it doesn't carry the sync signal. You will also have to somehow connect the composite video signal from the DVD to the SCART (it doubles as the sync for RGB).
Either way, the MX will not understand component, so you'll have to configure the DVD to output RGB, which is hopefully possible.
It might be easiest to use the S-video connection, it's still a lot better than composite - potentially even better than RGB, since the RGB switching in these televisions is regrettably pretty much substandard.
And a final problem, the MX may not switch to RGB at all unless you also have the RGB switching signal from the SCART, in that case you can only get composite through the SCART adapter anyway. There are plenty of ways to make this simple task complicated!
(yes, there is also such a thing as sync-on-green RGB, but the MX won't eat that either)