I have not seen this requirement anywhere, but it is somewhat implied by the way the BMW systems work. This is specifically advertised for someone who has a navigation system without a TV module. It would not really be designed for a car that had a screen and neither nav nor TV, and someone who already had a TV module would not buy it.

Yes, it does have the composite to BMW conversion, and I suspect that it emulates a TV module to the nav computer. However, when the TV module and nav computer are connected in tandem, the TV acts as a slave and expects the nav to tell it when to turn on. Therefore, if you have no nave as the primary, I suspect that this video module does nothing, since it probably always assumes that it is the slave.

This is all conjecture, since I have not seen one first hand. But it would be consistent with what I know of the nav and TV module behaviours.

__________________
SOLD
2000 E38 750iL Highline Edition, Upgraded with the lastest 2006 X5 Electronics
MKIV Navigation, 16:9 Display, Bluetooth, TV/Video with Backup Camera, Sirius, and Aux Input