I have heard both, the Levinson to me doesnt sound much better than the Bose in my Escalade, however the Harmon Kardon in my Range Rover is the best i have heard ever in a factory unit, one caveat, i have the same system in my Wife's Jaguar XK8 and it isnt near as good sounding, i would percieve this to be because of the space limitations.
Kurt
Kurt