There were three superpowers minis but sounds like you want the 6 issue series. Jack Kirby did the book and from what I heard is he used the mini to finish up his forth world stories! So if you are a forth world fan you may want to pick that up!cover art you come up with.
I had not heard of DC Challenge before reading your post, but just Googled it- looks pretty fun! I might have to check it out should I ever get through my insane backlog. Though maybe someone who already has it and wants to bind it will hit me up before I get around to it (hint hint!) I've not read Super Powers either,
DC Challenge was 12 teams each get a book. They make a mystery and end on a cliffhanger then the next team has to add to it. Tons of heroes show up and the joker hosts some of the issues! (he loves the parts where batman is in danger and breaks the forth wall and talks to plastic mans sidekick mid story!)