textsecure VS mixxx

I can't vouch for it, but this looks worth checking out: https://github.com/signal-golang/textsecure

So I think we need a native Linux client. I do not think Axolotl is a viable long term solution because it uses its own implementation of the Signal network protocol (written in Go). Reimplementing the cryptography and network protocol is a ton of work and will continue to be a ton of work as upstream adds more features. Axolotl has only just started reimplementing the new Signal groups protocol which was introduced 5 months ago. Also, the security of a reimplementation is dubious.

Mixxx is excellent and has pretty wide hardware support.

FYI the "limited" functionality of Rekordbox can be hardware unlocked with some Pioneer controllers.

https://mixxx.org/

There are quite a few DJs that use Ableton for DJing (or hybrid sets). Of course, Ableton wasn't made with DJing as its main function in mind but you totally can use it for that purpose and (with some tweaking) do everything and more that would be possible in a dedicated DJing software (like Traktor or Rekordbox or Mixxx)

I’ve used Mixxx a little bit and have been surprised how capable it is. It’s an open source project and is free to download: https://mixxx.org/

Mixxx (this one's free)

Mixxx

Related works: https://github.com/mixxxdj/mixxx/pull/4027

Mixxx (you already mentioned this; it's certainly a great piece of free software to test the DJ waters with and works with a lot of gear).

Alternatively, you can also use Mixxx with the S4 MK2. Mixxx is free. But instead of a Traktor control vinyl record, you'd use Serato timecode instead, as stated in the docs.

If the device is class-compliant, i.e. it follows the generic USB spec and doesn’t need drivers installed, it can work under Linux. However the free software you get with the controller (Serato, Rekordbox, Traktor etc.) won’t. The alternative is to use Mixxx. It’s free and open source. You can check their controller support. https://mixxx.org/

If you don't like any of those, aren't you glad you didn't spend the money to find out the hard way? There's more DJ software than those two, so try out these as well: Traktor Pro 3, Virtual DJ, DJUCED, or Mixxx.