Michael, forget the new amp bit. Your 1015 will supply the rated power, as it's legally required to do. A 140 watt amp would have about 0.67dB more capacity at momentary peaks than a 120 watt amp, e.g. 110.67dB compared with 110dB, which is insignificant. Your M60s use about 1 watt most of the time at a comfortably loud listening level and it's highly unlikely that even at momentary peaks more than about 100 watts would be used. Your 1015 is fine; relax.

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Enjoy the music, not the equipment.