For what it's worth, I replaced the motor mounts on my 2006 S500 4matic just a few weeks ago it's even WAY more simple than the service manual suggests.
I was able to do both sides in 2 hours and didn't need to mess with loosening the steering rack or removing axle shafts etc. Now that I know how it's done, I can probably do them again (next time) in about 1 1/2 hours..
The right side comes out from the top-
Just remove the serpentine belt, alternator mounting bolts and move the alternator out of the way so the mount will come up through the area normally taken by the alternator.
The left side comes out from underneath between the sub-frame and the engine oil pan (you need to remove the plastic cover under the engine bay). Just remove the 3 bolts that hold the cooler lines in place to the oil pan/block so you can move the lines out of the way (they have rubber hose sections so you don't bend any hard lines doing this) and you can snake the mount in an out from that opening.
For me, I removed the white rubber covers off the mounts just to make them easier to handle while getting them into position and then slipped them back on once I got the mounts into position (before bolting them down).
If you're careful, you don't even need to disconnect the battery (I didn't) and you will obviously need a floor jack to support and lift the engine slightly to remove/replace the mounts.
Probably one of the easiest jobs I've done on this car.