A. I do not understand why a single 8 ohm 500W Rumble 410 couldn't handle the 400W from your Rumble 800 HD.

Maybe the Gain, Overdrive, Bass, and/or Low Mids, or all four, were cranked too high?
2. If a single 500W Rumble 410 couldn't handle the 400W of your Rumble 800 HD settings, then I cannot imagine that a 300W Rumble 115 could even do as well. I'd expect it to blow! A Rumble 800 HD with a single Rumble 115 cab iwould only be safe for low volume settings.
iii. I believe you would need
three Rumble 115 cabs, reducing the power to just 267W each, to be able to safely handle louder Rumble 800 HD settings!
But, that's just my opinion. And I am a somewhat cautious fellow.
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