Yes, but only the i7-6700T.  The processors with a T at the end use way less power and generate way less heat.  The i5-6400T and i7-6700T both use 35W.  In contrast, the Core i7-6700K uses 91W.  The relatively small Alienware Alpha case and power supply were designed for 35W, not 91W.  Best of luck with the upgrade.