controling the level of radio/cd mute during nav guidence- how??

[Grantsmith82]

How do i control the level of mute when the navigation is giving guidence
e.g radio/cd either fully mutes, parts mutes or doesnt mute at all..

i dont have the nav-min option which use to do this on my e39 (which i lost after using navcoder- thats another story)

how do i do it on my 2005 E53 X5?

so far tried menu,set, nav volume ("louder" "quiter") this just controls the loudnes of the nav not the level of mute from the radio as it speaks..