Can I just play the audio signals from the other two computers and capture it with the mic, or is there a better solution for that.
It depends on what you're trying to accomplish. Are you trying to test the speakers of the two different computers, or just the output from their headphone or line-out jacks? If you need to include the effects of the speakers in your test, you'll need to use a microphone as you indicated. However, in that case, it may be difficult to know if any measured differences are due to the audio components of the two computers, or if they are due, in part, to the acoustical environment in which you are working and the positioning of the two computers relative to the microphone.
