Andre, welcome. Although the internet makes valuable audio information available, some discussions turn into a quagmire of misinformation. From your opening comments it seems as if you may have read something rather fanciful. The ideal of amplifier design is "a straight wire with gain", i.e., it makes the incoming voltage strong enough to drive a speaker, but adds absolutely no distortion or other unwanted effects. This ideal is impossible to achieve fully, but for many years it's been known how to design amplifiers at relatively low cost which have audibly flat frequency response and inaudibly low noise and distortion when operated within their power limits. Nothing more is possible, regardless of cost.
Although some discussions rather naively assign a "house" sound character to various makes(e.g., Yamaha is "bright", Marantz is "warm"), any engineer at a major manufacturer who came up with a unit that had an audible coloration would probably be immediately fired for gross incompetence.
The editor of the Audio Critic summarized this quite well a few years ago in
"Electronic Signal Paths Do Not Have a Personality!" .
We're in control of those features of receivers which do in fact change the sound, e.g., volume controls, tone controls, room equalization, etc., but the basic amplification process is audibly transparent. Buy a receiver on the basis of features and price, but there's no need to worry about an inherent "sound quality".
