N, pretty much the same answer as applied five years ago relating to your Onkyo 801: the 3311 can drive the M80s to beyond safe listening levels. The basic reason that it doesn't have an "official" 4ohm rating(magazine lab tests show substantial 4ohm capability for such units in real-world applications)is that it would have to pass severe tests, including five continuous minutes of full rated power operation into a 4ohm load under FTC regulations, for an unrestricted 4ohm rating. Relax and enjoy.
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Enjoy the music, not the equipment.