So I recently bought an NXS2 setup (both the CDJ2000NXS2s and the DJM900NXS2). One of the things that brought me to the NXS2 (to replace my Xone:4D mixer) is that the DJM900 mixer has historically been, out of the box, a great soundcard companion as well as a mixer.
This doesn't appear the case with the NXS2 variant. I don't know if it's just because it's too new or because Pioneer is trying to pull something with regards to forcing their software on users. I came from Traktor and to be honest, I really like the effects in Traktor as well as the ability to have a "live deck" where I can route audio right through traktor and utilize the effects without having to have traktor hijack my CDJs and turn them into controllers in order to get audio out.
I'm not sure how useful this mixer is to me without being able to use it like a soundcard like all the other mixers I've had since 2010 (and I've had several). Thing is, as of right now, Rekordbox DJ doesn't even allow you to use the inputs from the mixer (inputs meaning the ability to pass the signal of an item hooked to one of the mixer's inputs through the soundcard and into the software drivers so that applications can pull the audio in). I can't imagine it would be expected behavior to provide such a powerful set of hardware and have the drivers be the weak point.
I see all the other drivers are open source. I'm able to write/read C++/ObjectiveC and I wouldn't mind checking through the latest drivers to see if I can't figure out why the soundcard inputs only seem to work when rekordbox is loaded. I'm assuming there's some sort of information exchange that becomes available when rekordbox is started which is picked up by the driver to allow the stream of audio to flow (or perhaps audio is being ignored when the rekordbox isn't open?) It definitely appears the driver's engine is starting without rekordbox being loaded because I am able to output audio through the driver from third psrty applications and out through the mixer's USB outputs with no problem.