Al, welcome. You should be careful with your terminology; if you'd have said that on some audio boards which take this "bright/warm" thing about receivers seriously you'd be derided for not knowing that Marantz is supposed to be "warm", while it's Yamaha which everyone knows to be "bright". Seriously, of course, any of them would be fine with the M60s; any well-designed receiver/amp is transparent and neutral.

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Enjoy the music, not the equipment.