Depends on how you want to use the CDJ-2000s. You can use them with either the control CDs, or in native HID mode without the CDs. HID mode is better than the control CDs, so I'd recommend that. For HID mode, you need a powered USB hub unless you have a 17" Macbook Pro with 3 USB ports. Connect the CDJ's USBs to your Mac, go into the Utility menu on the CDJs and select Advanced HID mode, then select the deck. See this guide for more info... serato.com

In either case, the outputs of the SL3 have to go into line/CD inputs on the DJM-900. All the effects on the mixer will work fine.

Konix,

Thanks for the help. Does the USB hub have to be powered? I have a hub that directly connects to my Mac, which is not a pro (MacBook 2008, Software Mac OS X Lion 10.7.3), just by usb. If so, what type of hub would you recommend? Thanks again for all the help.

Also, I know that the DJM900 Nexus states this:

"Time Code Output – Through its USB port, the mixer can output time code disc signals for DVS (Digital Vinyl System) software6 when used with a Pioneer CDJ player or analog record player. DJ play using DVS software can be done without difficult and complicated connections7. (7Not compatible with Scratch LiveTM made by Serato)"

What exactly does this mean?/What is Time Code Output?
Sorry I am new at this!

You should definitely use a powered hub, a lot of us have success with Belkin.

The timecode output system in the 900 is not compatible with Scratch Live, as it says.

If you use Traktor Scratch from Native Instruments instead then you can hook up the system in a different way.

As you are using Scratch Live (a good choice!) it does not affect you at all.

Thanks for sorting out Mike guys:)

Yes, thank you all. Everything works perfectly!