We do not have mythtv 0.26 in LinuxMCE. The latest version is 0.25.
I don't think my question regarding composite was version related but it might of course be caused by the mythtv version... ;-).
0.25 missing stuff, with that version I had no way to get a working setup.
0.27 was working but very unstable.
so 0.26 seems to be the best choice. just have to get rid of the tearing.