Since these are audio recordings an easier hardware approach would be to tap the output of the motherboard's D/A converter right before the speaker amp and capt

Since these are audio recordings an easier hardware approach would be to tap the output of the motherboard's D/A converter right before the speaker amp and capture it with an A/D. You could also tap the speaker wires which should be easier than tapping thin SMD traces, though the signal might have been highpassed before amplication to better support the small laptop speakers. Of course this means you'll have to disassemble the ancient laptop and all that, and it won't be a bitperfect capture. For voice recordings though the quality should be more than adequate.