LK, welcome. Since you're using this in a(presumably fairly small)bedroom, it's highly unlikely that you're even using the 80 watt capacity of your 485, and since you're only using two channels, it's in fact coasting. If so, the distortion is inaudibly low and if there's a clarity problem it wouldn't have anything to do with the receiver. So no, spending more money on a replacement wouldn't improve the basic sound quality and wouldn't really be an "upgrade" in that respect.

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Enjoy the music, not the equipment.