Thanks RoHe for the pointers to the threads. After reading them, I have re-installed the legacy OEM fans in interesting places and used splitters to eliminate errors. It is all worth it to get rid of the stock heat sink. Sad to see the BIOS behavior change so much from the 8940 to the 8950. I am sure some genius or committee thought was a great idea to tighten OEM compat. Feels like Dell is drifting toward Apple thinking. 
I have upgraded the stock CPU fan/heat sink and rear fan to my XPS 8950. I used the Noctua NH-U9S and NF-A12X25 respectively. Both fans are not recognized by the BIOS and randomly throw errors for one or the other or both at boot up. Both fans run smoothly with the CPU running at optimal temperatures. I have done this same upgrade for a XPS 8940 that has worked well and has no errors. Is this an issue with the new BIOS on the XPS 8950 (I am running version 1.10.0)? If so, can Dell send and update to support common aftermarket fans? Great product btw. 
XPS 8950, 3rd party fan upgrades not recognized