audiofan,
You really have to watch what they do to those receivers in the stores (or at least keep in mind the possibilities).
It is possible the audio salesmen tinker with certain settings to make their higher priced units sound better. There are TONS of settings that could do this other than just treble or bass though. For instance, one could turn on the Yammy1400 unit where they tweaked the "centre channel width" in DPLII to shrink it down so the soundstage is reduced and more collapsed into the centre. Then they bring you over to the Yammy2400 where this setting is done correctly for the speaker spacing. The user would think "oh ya, this 2400 has a much better soundstage than the 1400" not knowing what a simple tweak will do to change that.
Other than SPL calibration when doing comparisons, this is by far my biggest concern when i walk into any audio store. That is why the ultimate test is best done at home where you can tinker with things yourself.
Worry more about your budget and required features, then take the unit home to audition it (most places have good return policies, esp. big box stores) before you decide 100% which unit you like. If you put some good cash and a bit of testing into the purchase, you will have a receiver for the next 15 or 20 years or maybe more that you know was a good decision as a buy.
