MartinR wrote:
I would try using Airplay. No cables required.
I looked into this some more today and Airplay by itself won't achieve what you want to do. Although it can stream audio to your receiving Mac, it will not not appear as an audio source in Quicktime. I tested it myself and that's that.
In order to use Airplay you would need additional sofware on the receiving Mac. Under normal circumstances Audio Hijack would do the job just fine - both to capture the Airplay stream and record to a file. I tested it on my Monterey Mac and it works perfectly. But unfortunately there is a reported bug in Sonoma & Sequoia that blocks Audio Hijack from capturing Airplay audio on those versions of macOS. The reported workaround by the authors of Audio Hijack is to use a different one of their products - Airfoil + Airfoil Satellite. Airfoil is $35, Satellite is a free add-on.
Blackhole Audio may potentially be able to route incoming Airplay audio to Quicktime but I haven't used it and cannot provide any help there.
Have you considered just using a single MBAir with both DJ and Audio Hijack on it to produce & record your DJ audio on the same Mac?
If you really do need/want to use 2 Macs, then in my opinion using an audio interface between the two Macs would be easier & preferable to going down a rabbit hole with additional software & system settings.