I have a MT-32, but I won't consider it for this thread... Here are my contenders. I think they stand a decent chance to pass the muster as oldest... We'll see.
1988 - Creative Music Systems (Later, Creative Labs) Game Blaster card
(worse than FM synthesis / Adlib, like a multi-voice PC speaker)
1987 - Covox Speech Thing (The original parallel port DAC itself!)
Here's a pic of the Covox:

