How to feed input into volumio

How can I add a sound input from my computer to play through my system? I would like to use REW software to do room/system calibration and need to feed the sweep audio from the laptop through the audio.

My audio system is as follow:
a RPI3B system running Volumio +
IAN CANADA FIFOPI Q7 Synchronous FIFO Reclocker +
IAN CANADA Dual Mono ES9038Q2M DAC HAT +
IAN CANADA IVSTD MKII Output stage module +
this feeds into an Elekit TU-8600S tube amplifier then speakers.

I can output sound from the MacBookPro 's 3.5mm jack but where do I feed into the audio setup? I can cast the sound via Wifi but is laggy/buffers, so prefer a wired connection.

Thank you all.

Since you have an Mac you most likely will have a iPhone?