Jason, there'd be no reason to expect a "clear difference"(or any audible difference at all)between receivers(regardless of price differences)when their amplifiers are operating within their designed limits. This of course doesn't apply when processing circuits which are specifically intended to change the sound, e.g., tone controls and room equalization, have been put into effect. So far as basic amplification, competent and conscientious engineers apply basic audio design principles which have been well-known for years to achieve transparent amplification, which results from audibly flat response from 20-20KHz together with inaudibly low noise and distortion. One of the great things about the modern audio scene is that this has been accomplished with even receivers of quite modest cost and listeners have no good reason to be concerned about their "sound quality".
Of course, reports to the contrary abound, but these lack the reliability of a carefully controlled blind listening test. In particular trying to "listen" to different receivers at a store is essentially meaningless even if the salesman hasn't taken steps to favor a particular unit. The volume between the different units will always vary at least slightly and the louder one will sound better, although it won't be apparent as a level difference, but will be described as "clarity", "soundstage", etc. This is why in blind listenibg tests a basic requirement is to adjust the overall levels to be identical within 0.1dB.
A good summary statement of this reality is found in the Audio Critic article
"Electronic Signal Paths Do Not Have a Personality!" .
DACs were also brought up, and it should be kept in mind that DACs are a mature technology, as Alan among others has pointed out several times. Excellent chips which perform the conversion without audible flaws are bought by manufacturers for as little as $1 each in very large quantities. The small measurable differences which still exist don't have audible consequences.
