Everything in 1999, it seemed, was all mapped out for Dream Theater keyboardist Derek Sherinian. The hard-rock quintet was to begin recording a new album this month; he had his involvement in a side project, the supergroup Platypus, whose debut Velvel album was released Feb. 9, and his solo debut LP, “Planet X” (on Magna Carta), is scheduled for a June release.

Then he got the dreaded phone call.

“Two weeks ago, (Dream Theater) made a change,” Sherinian said recently. “They just gave me a call out of the blue and said they wanted to use Jordan Rudess at keyboards, plain and simple. He was playing in Liquid Tension Experiment, another side project with (Dream Theater guitarist John) Petrucci and (drummer Mike) Portnoy. I know Jordan was their first choice when (original keyboardist) Kevin Moore split five years ago and for some reason Jordan wasn’t available, so they’ve had a relationship with Jordan for a long time.

“It totally came out of the blue. I played some holiday shows with them in December, and we were talking about going into the studio in February. There was nothing to indicate to me that wasn’t going to happen, so the call really did come out of the blue. That’s rock ‘n’ roll, man. You’re always a gun for hire, unless you’re the one that’s writing the songs and it’s your band. I don’t have any hard feelings toward them, I wish them the best.”

After the initial shock wore off, Sherinian began to feel better about his situation.

“The first thought is it’s scary because the mother ship is leaving you behind and you think you’ve lost all your superpowers,” he said, “but after a while, I assessed the situation and realized I’m going to be fine. I’ve gotten a couple of really cool job offers, and I’m going to explore them as soon as my record is done. One of them is an album and a tour with a pretty famous guitar legend.”

Jeff Beck, perhaps?

“Oh, I wish,” Sherinian said, laughing. “That would be a dream gig. This guy’s not that legendary, unfortunately. He’s the B-tier of legend. I’ll announce it later.”

Platypus was formed by Dream Theater bassist John Myung, who enlisted Sherinian, King’s X singer-guitarist Ty Tabor and Dixie Dregs drummer Rod Morgenstein. Their debut album, “When Pus Comes to Shove,” started off as an experimental affair but quickly turned into the real deal, fusing straightforward rock ‘n’ roll with psychedelia, metal and instrumental melodies.

To many listeners, the album will resemble shades of Deep Purple.

“The Deep Purple influence is probably there because I play a lot of B3 (keyboards) on the record,” Sherinian said. “While I was in Dream Theater, we did a monthlong tour with Deep Purple, and I got to listen to Jon Lord every night, who is awesome.”

In the liner notes, Sherinian thanks three early rock ‘n’ roll mentors: Buddy Miles, Alice Cooper and Kiss’ Gene Simmons.

“They’re the first ones to validate what I was trying to do,” he said. “They were the first ones to step up and say, ‘I believe in your talents, and I want to put you on the payroll.’ Buddy Miles hired me in 1988; that was the first time I went on a national tour and played in nightclubs like five nights a week, playing with a name entity. I listened to his (Jimi) Hendrix stories and about how he hung out with the Beatles and played with Santana; it was very important schooling.

“Alice Cooper was my first really big break in ’89 for the ‘Trash’ tour. It was very overwhelming. I was starving and living in Hollywood, and I was 22 at the time, then this job came through and all of a sudden I’m making all this money and touring the world and I’m on MTV. It was very exciting. It was a huge comeback for him, and I was glad to be part of it.

“Then I got with Kiss. Eric Singer played drums with them at the time, and he had played in Alice Cooper with me. They snapped him away and he said, ‘Why don’t you hire my friend Derek?’ I’ve been very fortunate to work with some legends.”

Sherinian joined Dream Theater in late 1994, a year after the group enjoyed the gold-selling success of its Atco album, “Images and Words.” Though he worked side by side with Myung in Dream Theater and Platypus, Sherinian said his ouster hasn’t affected their friendship.

“I’ve always gotten along best with John out of all the guys,” he said. “I have no problems with any of them, whatsoever. I’m really sincerely thankful for the opportunity they’ve given me and I harbor no animosity toward them. I want to make that clear. I’m moving on.

“What’s funny is, Platypus started off as a diversion. Right now, it’s my main gig. Ha! C’mon, Platypus! You know what? I’m just having fun with it. We’re probably going to do another record in a couple of months. I’d love to tour with it; I had a blast working with those guys. C’mon, Platypus!”

FIRST RECORD I EVER BOUGHT: “Aerosmith’s ‘Toys in the Attic.’ Great album.”

FIRST CONCERT I EVER WENT TO: “Van Halen in 1980, the ‘Women and Children First’ tour. My parents forbid me to go, and I ended up going anyway because there was no way I was going to miss it. I left a note for my parents saying, ‘I know you told me not to go and I know I’m going to get punished, but there was no way I was going to miss Edward Van Halen’s guitar solos, so punish me as you will. See you tonight. I assure you I’ll be safe.’ They grounded me for a couple of weeks, but then they let me off the hook.”