As you can read in some postings above, you won't get 100% YUV without modifiing the hardware.
For 100% YUV quallity you must change some capacitors on the mainboard (see the pictures in the postings above). But unfortunatly this modification will change the behaviour of RGB as well.
dreg: Components ?
EDIT : gefunden, /usr/lib/enigma2/python/Components...
Funktioniert. Danke
EDIT 2:
Die Datei ist "AVSwitch.py",
Ändern: Line 76 ( bei einem CVS vom 30.12.06)