I learned through mjuch trial and error that most cheeses can be blended into a dairy base such as cream or milk. The trick to it is patience. That is, the liquid should be no more than 180 degrees or so. And the cheese should be freshly grated. Add the cheese a little at a time, taking care to stir it until it melts into the liquid so that they are completely belnded. And remember, the stronger the cheese, the less you have to use to flavor the mac and cheese.
Cheeses I prefer to use are gruyere, fontina, a strong swiss, five-year aged white cheddar, muenster, parmesano-regiano, and colby. I have made my own Velveeta-style cheese by combining swiss, cheddar, and jack cheese, with salt. Again, I used hot, but not boiling milk, and grated the cheese into the liquid while constantly stirring. I really enjoyed tailoring this cheese mixture for my mac and cheese, and for various cheese sauces. If you look on the Velveeta packaging, it lists whaat cheeses are blended to make the product. It is so soft because of the extra moisture from being blended with milk.
You can also use young cheeses like Mozarella that's kept in a water bath, or feta cheese. And cream cheeses are a nice addition. But the single most important factor in your mac and cheese is the flavor you like. You have to develop your own recipe. I like to add a little truffle oil to my mac and cheese. But then again, I almost think I'd add truffle oil to ice cream.
And smoky is a great flavor addition, as can be various peppers, or onion, or chicken broth, or, or, or... Try different things. Throw some pepperoni chunks into your mac & cheese, or some keilbassa. Try it with bits of cauliflower, or brocolli, or artichoke hearts. You just might surprise yourself with what you can create. I would think that a cheddar based mac and cheese would be phenominal with some slow-cooked beef roast slices mixed in, like a cheddar beef sandwich, but with pasta instead of bread.
I could go on with ideas, but it's time for me to go home.
Seeeeya; Goodweed of the North