I personally leave the "surround" setting off since it activates a DSP chipset that either emulates DPL (dolby pro logic) or some variant. In other words it turns a 2-channel audio track into a 7.1 presentation. The vocals and most of the font left/right is "blended" into the center channel speaker (center speaker on top of the dash), etc. Thus, unless you are watching a DVD while on the road (with the hack) or parked you are probably better off with "surround" disengaged.
As for the bass, boy you have a completely different experience than I do. I am constantly adjusting the bass (mostly turning it down) depending on the CD, DVD-A, or FM station in my GS430. For the FM radio I barely have it 2 to 3 "clicks" above "zero" of the EQ. However, for most CDs or DVD-As I have to lower it to "zero". In other words the ML bass response in my GS430 is fantastic and the ML is one of the things I love about the car. I can put in one of the worst produced CDs of all time and get the ML to render it quite well - way better than the stereo in my previous GS400. Of course on the other hand well produced DVD-As, e.g., Steely Dan's Gaucho is just absolutely flat out amazing on the ML.