Yup..

In order to modify psp 3000's the official firmware on it must be 5.03 or lower.. Then you can use chickHEN R2 to enable custom firmware on it and install 5.03 GEN C..

Now since you have a 6.20 official firmware on it, your S.O.L. for now, i suggest selling your PSP and getting one with a lower firmware or just wait it out till support for it or a downgrader for it comes out..