If any further proof is needed of how the jazz market has spread, consider this: Steps Ahead, a quintet coming to Blues Alley tomorrow night, has a Brazilian pianist whom the group's Puerto Rican-born bassist first heard in Paris. True, that bassist grew up in New York and the others who make up Steps Ahead are from New Jersey, Philadelphia and the Bronx, but it is in Japan, where they have released three albums, and in Europe that the 3-year-old group is best known.

Used to be that jazz players in the same group were generally of somewhat similar musical backgrounds, but the membersSteps Ahead, whose ages range from the early twenties to the mid-forties, come from all over the jazz spectrum--from swing-era and rock-style big bands; from bop, hard bop and free-form combos; from fusion groups; and even from associations with pop artists like Joni Mitchell, Ringo Starr and the Cuban superstar Celia Cruz.

Vibraphonist Michael Mainieri, who joined Buddy Rich's band as a 17-year-old in the mid-'50s, explained how the group first made it in Japan. "We had only played in New York twice, just pretty much to jam, you know, a whimsical thing that I had put together. A couple of Japanese critics heard us at Seventh Avenue South and raved about the band and then they asked us to come over and do a tour. I think it was a combination of us going back to the acoustic sound and the fact that they felt responsible for discovering us, too."

In addition to Mainieri, the quintet's principal writer, Steps Ahead consists of saxophonist Michael Brecker, pianist Eliane Elias, bassist Eddie Gomez and drummer Peter Erskine.