I have NEVER turned it up past about the second notch. The walls shake at that point. Actually that's not quite true. I did once take it all to a friend's open-air birthday party. We had it one-third-way up, but blew out a couple of woofers in his field.
Speakers are 8R, but that's what the system is designed for. V=IR, P=VI etc, so speaker impedance is actually irrelevant since amplifier output is matched to the speakers. Yes, about 2000W "music" or "peak" power (I hate those terms, so imprecise)