Bob, if you consider the Onkyo M-504 manual to be "valid info" and if you bother to take the time to read it, as I have, you'll find at p.4: "Only use speakers with an impedance rating of 4 ohms or more with this unit". The reason that the M-504 doesn't show an "official" 4 ohm power rating is that in order to do so under FTC amplifier power regulations it would have to drive a 4 ohm load at the full rated power for at least 5 continuous minutes, which few units are designed to do without overheating. In real use, you may find, as have others, that the M-504 not only "likes" 4 ohms, it loves it!

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Enjoy the music, not the equipment.