You have not mentioned where the DMX chips fail...I presume it would be the splitter.
Please check for AC mains leakage onto the DMX lines (most likely from the fixtures). Make sure that earthing is done ONLY AT ONE END....preferably at the console end. I am not familiar with MARTIN splitters but check if they are optically isolated.
I have always stressed on the importance of investing on a really good splitter to protect one's system. I have nothing against any particular brand but the way to go in good setups is to use stuff like Avolites, Light Processor or Swisson. Bit expensive but worth it in the long run.