Aoki invited 6-year-old Jamar -- who goes by his nickname, DJ Masterpiece -- to visit his Las Vegas home for a playdate and a piano duet ... along with a private tour of his mansion and some fun in Aoki's Playhouse.

Thanks to the Kids Wish Network -- a charity that grants wishes to children with life-threatening illnesses -- Jamar and his family were flown to Vegas to spend some time with Steve ... and the aspiring DJ definitely learned a thing or 2 from the famous one.

The new pals also signed each other's custom matching DJ Masterpiece t-shirts, and Jamar got to let loose in Aoki's fun home gym ... equipped with a floor trampoline for some leaps into a massive foam pit.

We're told Steve also had some Aoki swag for Jamar and his family, and he's got a big surprise in store for DJ Masterpiece to encourage his love of music ... and it's certain to make the kid happy.