I had a wrestling radio talk show in college and me and my co-hort, the new GAF member MacstarX created the names as monikers for luchadore characters. Total wrestle-nerds. They more or less stuck and I use it for everything.
We initially added the X years ago because you'd be surprised what people have as their usernames....
fake edit: I know it's actually bastardized Spanish.
Crow Phoenix came about around the time MST3K was ending.
Crow, of course, comes from Crow T. Robot. While Phoenix comes from my desire to see the show feature a rebirth. The fact that the show was reborn in Cinema Titanic, Film Crew, and Riff Trax is an awesome bonus.