I experimented and took an iPod speaker splitter wire—to plug iPod into analogue stereo—and merely swapped the configuration. (Took me a VERY long while to arrive at a solution via Occam's Razor). I plugged it into the speaker output vs input—duh! I thus reversed the connection, and then plugged iPod headphone end into my MacBook line in. Half-way there. I then found a program that would record off the desktop. WireTap (old v.) will work, or open source Audacity, as does CD Spin Doctor—usually bundled with Toast. Mad audio scientist at work with no manual, as usual. We don’t need no stinkin’ instructions.
What I’ve learned is that, if you can get a sound register via the line-in, then, you can record anything, LPs too. Not great quality, but worth a try if the music is obscure enough to not make it to the digital age. I'm salvaging my old audio tapes first—obscure sean nós Irish singing tapes—most of which don't exist in digital format. Saving old audio cassettes from obscurity—bringing them into the digital age before they turn back to base iron—has been a bit of a journey with no map. But the relative obscurity and rarity of these songs makes it worthwhile to go the extra miles.
Somewhat expanded and revised for clarification from two Facebook posts, added 6/21
