CDJs in HID mode w/ Traktor?

You only need to worry about aggregate if you have a mac, which you are if you’re on a windows laptop it’s plug and play. Aggregate set up is to tie the in built sound cards of the CDJs together to make one sound card. However, as they have a 900nexus mixer you may not need to as this also has a sound card and is also midi.
I have the CDJ900 but use windows and it was just plug and play but I don’t use Traktor anymore. Another option you have is to download a copy of RekordBox from PIoneers web site, analyse your music, make some playlist then put the on a USB drive. No need for the mac just take the drive and plug into on of the decks and it’ll be share across the link. Easier than taking you’re mac. Head over to the Pioneer DJ Forum for more info on aggregate set up for your mac. You’ll love the 900s and nexus mixer don’t miss the chance to use them.

If you going to use Traktor I’d go with using the CDJs as the controller rather than the mixer especially now that 2.5 supports advanced HID and give you a wave display on the CDJ. I’d set Traktor to external mode and use the nexus FX. The other option, I’ve used it live, is to use RekordBox via the Ethernet link. I would only recommend this if you find that’s it’s stable, it can play up. When linked you get 2 CDJ icons and you can just drag n drop you tracks in and they will load in to the CDJ or you can you the scroll search function on the CDJ to search through you collection.
For me Traktor was a means of accessing a large selection of music and being able to play it. Burning CDs is a pain. I never really used the in built FX once I moved from a controller to multi format players so when got the 900s I no longer needed Traktor as I had .
You’ll find plenty of info about RekordBox, the CDJ900 and 900nexus on YouTube and quick answers over at PIoneer, I also use that forum. Also take a look in the mix section here and I’ve got a video of me using the the CDJs and RekordBox