Not sure if it's the first one, but the one with the oldest timestamp (April 1997, which seems about right) still on my computer is this:
...followed by this:
I believe I downloaded Napster with the intention of finding Das Boot by U96, as per the Now Dance 92 CD version, some time around 1996.
I stand by this choice.
I also remember when MPEG Layer 3 was vying for DVD supremacy of Dolby Digital 5.1. As such I think I bought Jerry Maguire on DVD with and MP3 soundtrack.