My "TEMPORARY" solution has been to use the new 7" Magellan GPS unit, it works well but the mounting is not so easy on the eyes a bit crude but "TEMPORARY". I used Velcro to attach it on the dash. I look forward to an aftermarket unit that looks like its a BMW unit.
My 2010 335i has an excellent factory BMW GPS, 10" diag. and works and looks great.
I'm looking forward to unit specifically made for the E53, here's the
DYNAVIN web site
Dynavin