Comentário oficial
All CDJs are USB2 host ports, but all USB3 devices are backwards-compatible and can be read in USB2 hosts.
There is no benefit to the CDJ having USB3 speeds as the maximum (theoretical) bandwidth of USB2 is 40MB/s, and even if you played the highest quality songs possible on four linked players all from that one USB drive, it wouldn't get close to 40MB/s.
Where USB3 is desirable for a USB device is when exporting from rekordbox; faster drives = faster write speeds = less waiting.