Redirect Audio from PC to Mac
My goal: to simultaneously play the audio of both a PC and my Mac to a single sound output.
Solution 1: Audio mixer panel
The most reliable way is to purchase an audio mixer. The advantage is that the delay is likely negligible, and it is easy to adjust the relative volume. The disadvantage is that you can't easily use a Bluetooth headset. Although some mixers have Bluetooth, most have only Bluetooth input (for a microphone), and even those that do, are not capable to sending feedback (like pressing the adjust volume keys on your headphone) back to a computer. So this solution is nice when making a (semi) professional recording, not so much for home use.
Solution 2: Play through with Quicktime
My preferred solution is to send the sound output from the PC (using the blue/cyan port on your PC sound card) to the line in input on my Mac, and then redirect the line in to the line out.
A few software solution exists that can do this, including QuickTime, Garageband, several applications by Rogue Amoeba, and the open source command line tool `sox`. The difference between the different solution is (a) the amount of buffering, which may lead to additional delay, and (b) the option to adjust the volume.
The QuickTime solution works by:
1. Open QuickTime player on MacOS 10.6 or higher. 2. From the File menu, select New Audio Recording. 3. Click the expand triangle (next to the record button) and select Line in as input/ 4. Set the volume using the slider.
The advantage of this solution is that it is free, and has volume control.
An often mentioned disadvantage is the additional delay that is added. If this is an issue to you, check one of the other solution mentioned at https://superuser.com/questions/58188/is-there-a-way-to-listen-to-the-input-sound-on-mac-os-x, including GarageBand, sox, and Audio Hijack from Rogue Amoebe. Audio Hijack is very nice, but is priced at $60 (USD) excluding VAT. The former (free and very simple) LineIn application from Rogue Amoebe is no longer supported or working on a modern macOS.