Change in picture when using digital out

Strange thing, I have a Pioneer DV-575 but I would had thought the DV-696 and the new DV-600 are similar as they have the same settings.

My player is NOT connected to an amp, however if I have digital out set to on (in initial settings) my picture is darker but more solid looking, if I turn digital out off, my picture gets brighter but thinner looking!

Surely this shouldnt effect the picture.

Anybody else noticed this.. or... if you have a similar player, could you test this out?

Thx