I've an E39 BMW with analogue tv/satnav, mk4 unit. I gather there is a way to upgrade this for digital tv (i'm in the UK) but can't find out where to get the necessary parts, cost of how to fit it. IS it a simple unit change or what? Can anyone advise?

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BMW 530D Sport (2001 UK)
SATNAV Mark IV DVD
OS 4-1/91