Hi Gueneter,
With further investigation; I see that the ADV7611 demo board has an ADV7125. The devices are connected together; with ADV7125's SYNC# tied to GND and BLANK# tied to VCC.
The ADV7611's HS and VS signals are then tied to the VGA connectors.
I plan on doing something very similar ... is there any downside to pulling BLANK# high?
-Matt