You could use Dante with DVS (Dante Virtual Sound) over network on each Mac. You would need to buy two licences for DVS.
You can also send audio/video over NDI. In QLab Settings - Audio you can create new Audio Patch which uses NDI (I think you may need to create a video patch using NDI first). On the second Mac you would create an Audio input patch using NDI. that is probably the simpliest way as requires no extra software.
No sure why you would want to send audio to second Mac rather than direct to your sound system (unless this is for streaming service) ?