Hrm,
Consider this:
Most cars have background noise at 70 mph greater than 70 decibels.
Even luxury cars are in the 65-68 db range, with all the extra sound deadening material helping to insulate against the NVH (noise, vibration and harshness) demons.
You'll have good sound, but never will get the sound you have at home... unless you go parking.
-PCM