
The CDJ-3000 is not compatible with rekordbox 5, because it was launched after rekordbox 6 was already released.
So when a new product is launched, a new rekordbox update is released to add compatibility for the new product. Then all future updates and versions of rekordbox from that point on will work with the new product.
But you do not go and add compatibility for older version, as they will become obsolete anyway.
And rekordbox 5 is an obsolete version now, for which support has stopped.
So if you are using rekordbox 6 and encountering some issue, then please file an inquiry ticket here and our support team will gather some additional information to assist you in resolving this issue.