Snow, welcome. The good news is that the concerns you've expressed are almost certainly unnecessary. Unless your particular unit is defective, the 6006 is easily capable of driving the M80s to beyond safe listening levels. The red light doesn't mean that you're "using wrongly rated speakers", but most likely indicates that an intermittent short exists in the wiring. Examine all the external wiring connections, but even if they look good carefully redo them. This type of problem in the past has often proven to result from a loose strand of wire making contact and causing a short. A more remote possibility is an internal short in the wiring of one of the speakers. Check for this(if the problem still exists)by disconnecting one speaker at a time to see if the problem doesn't appear when it's not connected.
The M80s are being used successfully every day with receivers less capable than your 6006, so again, unless the particular one you got is defective, it's not the problem. Very few receivers can pass the FTC required tests for an "official" 4 ohm rating, but nevertheless they do fine in the real world of home listening outside the testing lab.
