Greg, a couple more points. Since we don't know the cause of the "protection mode problem" yet, there's no purpose in discussing spending more money on a guess.
You say that the EP500 line-level inputs "don't work", but do you mean that the external input jack is broken? If so, the output jack works just as well to input the voltage, since it's connected to an internal "Y" arrangement which leads into the sub amp.
The closest approach to your request for comparative results using the lower impedance setting would be in the December S&V test results for the
1008 . Although your 3008 has a bit stronger amplifier section and should handle the M80s with even greater ease when properly set up, the effects of using the 4ohm setting are clearly shown, and would be similar in your case. Note that in one and two channel tests the 4ohm results of 272 and 229 watts were reduced to 65 and 45 watts at the 4 ohm setting. This may not be the only cause for the problem, but voluntarily cutting the voltage output capability certainly doesn't help, and this setting should never be used.
