David, welcome. There's no need to be concerned about how your 2150 will "pair" with various speakers; it's a fine receiver and there's nothing about it which would make it less suitable for certain speakers. As to whether you'd like the M50 or M60 better, there's not a major difference, but apparently the M50 is slightly more laid back. Most likely owners of each will comment.

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Enjoy the music, not the equipment.