So curious about the difference between the two cables.

1 - stock BMW OEM cable is just a simple cable which fits between the BMW TV tuner and NAV unit link shown above. This would only serve as a simple interconnect between the NAV and OEM TV tuner.
2 - modified from stock BMW OEM cable with the analogue connectors already attached. (which is the one I am using in my E46).

In my "old" E83 setup with the Gnet video module the cables to the NAV went to the video module and the video module had a second harness going into the NAV. My new video module has a similar set of cables but in addition has an IBUS interface but is using a VGA input and passthru. The RGB video is very tweaked in that it "appears" to have a higher resolution than the analogue video input on the E46 OEM TV tuner input.

I found the cable that I am currently using in the E46.

ToysInYourCar.com - AV Input/Output Lead

Theoretically can I still add a newer digital tuner (smaller) to the same setup (old IBUS) on my E83?

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E83 - Aero PKG Mods installed: Homelink mirror. CIS-IBUS video module, AUX, Rr Dr Release, stock wheels, Remote start, CarPC (Atom) & mud flaps - NAV - MKIV - NA Map DVD - 2011
E46 - 18.5 wheels/tires (summer), 17 stock (winter), Homelink, NAV software upgrade, BMW video module, Radio to V53, AUX, USB IBUS interface,BMW alarm install, CarPC(Epia), remote starter, tank battery & angel eyes. NAV - MKIII - NA Map CD - High Version 2008.1