Sure, 7 strings have fairly recently become popular, especially with headbangers. But an 8 string acoustic? Before I heard this at the time last year, I had never heard of such.

direct audio link

I'll warn that it's from our Public Radio classical station, thus the interview isn't the liveliest, most energetic ever for sure. But when they play, the audio is clear...unlike Youtube. On this day, there's actually 2 guitarists each taking turns playing a song. The 1st is the 8 string, at 5:30-10:20. And should you be interested, the second guy's song (on standard 6 string) is pretty cool too, at 16:00-19:40.