The line-up change comes before the band embark on their first US tour of the year.
The two departing members left the following statements on the band's website.
Quaid: "To the fans and comrades all over the world, thanks for letting me and us live this dream, it's all I ever wanted, but now all I want is at home."
Cash: "As much as I love the band and the music we make, it's just not worth sacrificing my home life. So now, everybody wins: the band gets a touring keyboard player/driver/roadie who loves his job and I get to be home in Louisville and spend time with my family and friends and start my own business."