I absolutely agree that the pre-pro has a much greater impact but I would caution that even slight "coloration" is generally present with every amp. The "golden ears" audiophiles that claim to hear wide differences in sound are easily dismissed as part of the fringe, but even mainstream researches / inventors has docuemented that changes that occur as the power supply of an amp heats up / draws more power / encounters a more challenging load result in changes in the audiable portion of the sound spectrum. Back in the early 90s Bob Carver spend a lot of time analuyzing the various ways in which these difference would be noticed and even marketed some amps that had, in his terms, the characteristic "transfer function" of other amps. Some of these sonic colorations are subtle and have more to do with time delay characteristic than traditional injections of spectral distoration but even live performances of amplified music are not immune from the tonal ephmasis / coloration that happens with different amplifier designs...