I have to set the F/R balance on my ML system about 3/4 of the way towards the rear so that the front speakers don't overpower the rears at the drivers seat position. Do you guys have to make this much adjustment or is there something wrong with my amp?

 

I don't have the ML system, but having to put it "3/4" of the way towards the rear sounds a little extreme. I think I faded to the rear about two clicks off center

 

That sounds about right. I have the same OCD and I do that to all of my cars to make the sound feel more balanced.

 

The sweet-spot will vary based on driver height and seat position.
Typical settings are one click to left and two clicks to rear.
As the subwoofer is in the rear... rear/strong is better.

 

Yes I was agreeing with you and elaborating on the physical properties applied.
Inside an automobile where the subwoofer is in the rear, it is unbalanced... To achieve balance, stronger rear audio is better. Simply because there is little bass in the front.

 

Lexus prefers their sound staging in front of you so if you want have more of a surround sound effect you will need to fade back quite a bit. There is nothing wrong with your Mark Levinson. Your system has 90% less distortion than the factory standard. It has a balanced subwoofer not a boom-boom type. It will shake the rear view mirror to a blur on bass heavy selections. Put a DVD with a good soundtrack in and depress the parking brake and you will get some great spatial effects from the five channels. The RC ML has Clari-Fi which is a proprietary decompression technology to restore lost information in Bluetooth, MP3 and Satellite broadcasts. You made a great decision opting for it.