S-Class Guru has remarked on the thought that occurred to me as I read the symptoms you described, particularly that you could jump the aux fan and that would keep your temps under control. Low fan speed is triggered by a pressure sensor set to actuate the fan at 20 bars (or is it 15?) of compressor pressure, while the high speed fan is triggered by a temp sensor set to actuate high fan at about 105C. Given all of the other repairs to the coolant system, I'd go straight to the 2 sensors responsible for aux fan operations.
Additionally, Jim Forgione has devised a clever little device called Cool Harness, designed with Mercedes' known overheating tendencies in mind. Search this forum, there are threads. It functions by actuating the
high fan speed at either 92C, 95C or 98C of coolant temp (depending on which variant you buy), regardless of what the A/C is doing at the time (i.e., whether the low fan is on or not). In other words, it starts the high fan some 8-15 degrees before the factory specs would start it. Installs very easily in place of the bipolar plug coming off the CTS. If you're interested, his website is at this URL:
http://www.k6jrf.com/MB_S500.html