
The DJM-750MK2 is a 24bit/48kHz device, so I expect the original 750 is the same (not 96kHz).
Audacity doesn't support ASIO devices out-of-the-box, you either have to compile a copy with ASIO support or use a 3rd party tool to convert the ASIO signal to another Windows audio driver type.
I haven't used Audition so I can't tell you what or where to configure it, just that you can likely find the audio settings all in one place.
The only settings to configure in the utility would be which channels you want outputting what signal: