Yes, but the computer doesn't have the firmware to "record" that signal from the speaker output pins. Thus, to record from the speakers acting like microphones,

Yes, but the computer doesn't have the firmware to "record" that signal from the speaker output pins. Thus, to record from the speakers acting like microphones, would require rewiring the headphone cable, for the vast majority of computing devices. If you click "record" on your computer, there's no way to tell it to record signal from the speaker output channels, even if you write a custom low-level application directly making OS calls. The OS can't even do it, because it's not supported by the firmware.