Guilty as charged! I installed 3 8" dual 4-ohm subs and went looking to see if anyone had already done this for an amp rated at 500W RMS at 1 ohm, that's when I found both threads. Not starting any trouble, just learned something and wanted to share.
I know this is waaaay late, but I see this question a lot. I won't bore you with the math, but I used nonlinear regression and the specs at 1,2, and 4 ohms to estimate the watts RMS @ 2.67 ohms. You theoretically should get about 991 watts RMS; the R-squared value is not ideal, but it's close enough to 1.0 be confident in the formula Excel spit out. Hope this helps someone...