Co, welcome. Your description of the listening conditions that you observed illustrate the problems in trying to "audition" even items which differ significantly in sound quality, such as speakers. Even well set up systems will often vary at least slightly in their positioning and adjustments, invalidating any comparison.
A still more basic factor makes attempting to "listen" to receivers rather pointless: if they're correctly designed(as nearly all are these days, even at relatively low pricetags)they'll all provide transparent amplification which is audibly flawless when all factors are held equal, especially sound level(rarely done). Select a receiver on the basis of features and price, but don't imagine that "sound" is realistically a determining factor.
