Cassaday and Joss Whedon's celebrated run on the title has been transformed into an animated webcomic, debuting this week.
"I think Astonishing X-Men has a filmic quality to it and could translate well into another medium," Cassaday told Newsarama.
"It's also accessible to audiences who don't read comics and keep up with all things X. That was one of our goals when we approached the series and I think it serves the motion comic well.
"I'd seen some other motion comic animations and the quality varied, so I was initially hesitant when Marvel asked me to be involved, but after looking at some test footage and hearing how committed they were, I joined in.
"It's a sharp confident soap opera and epic in scale. Joss's dialogue goes a long way when you're bringing something like this to life. The characters need to sound real and believable. You must be invested in them and care what happens to them and Joss is a master when it comes to that."
The Astonishing X-Men motion comic goes on sale on iTunes on October 28.