The late 2012 iMac update simplified the analog line-in/out and headphone jack. Moving from a MacBook Pro to this iMac, I am now unable to record with my external dynamic mic and small Mackie mixer plugged into the headphone jack with an RCA to 1/8" cable. In the Sound preferences, the line-in does not show up as an input option, only the internal mic.
The most popular solution I've found is the obvious one, namely, get a USB audio interface. But I do so little recording that it seems silly to buy another piece of gear to functionally do much of the same as my mixer does already, and I am not interested in doing so.
Is there another solution to this problem? A mono cable (which is fine for voice recording) or a TRRS cable that makes my iMac think a compatible mic/headset has been connected? Clever and outside-the-box ideas are welcome.