I also run 19 inch AMG split rims on mine, I inflate the fronts to 2.4 BAR and the rears to 2.5. These are the pressures recommended by Mercedes as illustrated on the fuel filler flap for 18 inch wheels.
Hi Alastair, my S600lBiturbo has factory fitted AMG 19" alloys. The sticker on the fuel flap states for 3 persons front 2.6 bar and rears 2.7 bar. Fully laden 2.8 and 3.1 bar.