I don't think that Kevin Max went secular in his music career. I have never even heard a hint of that. Last I knew he was singing for Audio Adrenaline, briefly. Anyway, you can check this interview out when you get a chance.
http://www.crossrhythms.co.uk/articles/music/Kevin_Max_The_Imposter/21535/p1/
As far as DCTalk being at the height of their career, I don't think that's true either. As the article stated Jesus Freak sold 1.7 million and Supernatural sold only (right, only) a million. While that's a lot and they could have done another album and seen what they could do with it, it was also a great time to go solo. Toby Mac has done quite well for himself in the Christian music market, and Mike Tait is, last I knew, singing for the Newsboys. That's not a bad gig, right? I think if they'd done another album it would have tanked and the opportunity to go solo would have passed. That's my take anyway.
Just for the record, I was a huge fan of DCTalk. I saw them in concert no less than 5 times. Twice for Jesus Freak and twice for Supernatural. Once, my wife and I saw them in a bar in Kansas City where Sixpence None the Richer opened for them. That was pretty cool.