Andre, the M100s are of about average sensitivity(1 watt needed for 88dB at 1 meter)and have no unusual power requirements. Don't think that bigger speaker means bigger amplifier, because there's no necessary relationship between the two. Often a smaller speaker may be of lower sensitivity and would need more power for the same sound level.
Even 10 watts would make the M100s "sing" at a quite loud level about 93dB per speaker at a typical listening distance. The 125 watt rated X4000 has a fine amplifier and should have ample capacity for brief peaks at high(but safe)listening levels.
