DDJ-SX with CDJ900, Serato DJ and Scratch

Hi I have got a DDJ SX and one backup CDJ900 and I tried to plug my CDJ900 into my laptop and use it with Serato DJ but it doesn't show any information or even let me put songs directly from the software to the CDJ. I'm not sure about putting songs from laptop to CDJ but I am sure you can see the data of the CDJ on Serato (Scratch), however DDJ SX doesn't really work with Scratch. Any recommendation?