It will have lower watts per channel at higher ohms. In a perfect world amplifiers will double their wattage when the ohms are cut in half. Some amps will but most won't. If a receiver is rated for 100 watts at 6 ohms then its 8 ohm rating "in a perfect world" would be 67 watts by my calculations, but its probably closer to 75 watts just guessing. In my opinion manufacturers who only give a 6 ohm rating are being a little shady, but it happens often.