I've read several articles about electronic modifications that claim to improve the sound of an amplifier. The primary factor seems to be the filter capacitors. Higher quality caps (with higher uF) really seem to add bass and warm up the sound. Also, the Pioneer amp design is a MOSFET system which *may* induce a significant difference in sound compared to other systems. I would think the quality of electronic components used in a system could affect its sound considerably.
The general consensus on many a forum seems to be that if it costs more and has more power, then any amp that displaces a previous amp sounds better. But is that really true? Or is it more along the lines of the person has spent alot of money, so of course it sound better? But I've always thought it was the speakers and room acoustics that affected the sound more than anything else.
This link, while rather technical, is pretty informative:
http://sound.westhost.com/amp-sound.htm
And I quote from the article:
"Speaker - Amplifier Interface
Many is the claim that the ear is one of the most finely tuned and sensitive measuring instrument known. I am not going to dispute this - not so that I will not offend anyone (I seem to have done this many times already), but because in some respects it is true. Having said that, I must also point out that although extremely sensitive, the ear (or to be more correct, the brain) is also easily fooled. We can imagine that we can hear things that absolutely do not exist, and can just as easily imagine that one amplifier sounds better than another, only to discover that the reverse is true under different circumstances.
Could it be the influence of speaker cables, or even loudspeakers themselves? This is quite possible, since when amps are reviewed it is generally with the reviewer's favourite speaker and lead combination. This might suit one amplifier perfectly, while the capacitance and inductance of the cable might cause minute instabilities in other otherwise perfectly good amplifiers. Although it a fine theory to suggest that a speaker lead should not affect the performance of a well designed amplifier, there are likely to be some combinations of cable characteristics that simply freak out some amps. Likewise, some amps just might not like the impedance presented by some loudspeakers - this is an area that has been the subject of many studies, and entire amplifiers have been designed specifically to combat these very problems [1]. "