Why is the interface 16-bits and the DAC 14-bits in the MAX5868?
The noise floor in the system is determined by both quantization noise and thermal noise. The interface is 16-bits to ensure the DAC noise floor is dominated by thermal noise instead of quantization noise. If the interface were only 14-bits, the quantization noise would increase and adversely affect the performance of the DAC as it would start to dominate the thermal noise.