Frosti, welcome. This point comes up frequently and you can look at the Sherwood 770 thread for a relevant discussion by Alan and others. The answer is that no, it doesn't "officially" support 4ohm speakers because the lab torture testing that would be necessary wasn't or couldn't be done. Nevertheless, the 6190 wouldn't know that it was connected to speakers that were rated at 4ohms and there's a high probability that it could supply the voltage and current necessary(the M80s are slightly above average in sensitivity and so require less, not more power)unless played unusually loud and long.
