You would be correct in your second statement. If the presentation of Yamaha receivers left you cold it is for one of the following reasons.
1.) You had heard or read that Yamaha receivers have a "cold" sound to them, and you mentally decided they should sound as they had been described, and you mind played tricks on you (this happens to most people)
2.) The speakers used had a "cold" sound
3.) The acoustics of the room may have caused the effect of "cold" sound
The biggest differences from amplifier to amplifier are headroom, wattage, and damping factor. None of these factors can alter the sonic signature of an amp to make is sound cold or warm, only additional circuitry will change the signature.
And I will stop here, because I must sleep.