Well it depends what you want them for-Do you want them purely for music,movies or are you hoping to make use of a mic as well? The m40x are monitor headphones so they "should" have a more timid low range (bass) but I imagine they would be amazing in terms of overall sound quality. I personally have not used the Cloud Alphas but if they are similar to the Cloud revolvers they would be great. The revolvers have a punchy bass, good overall audio and the mic is not bad either.
What is your overall budget and where are you going to be purchasing them from? Also main use-music, gaming and do you need a mic?