expanding upon noway1's good post, unless you have a properly treated room I think most source equipment ends up being largely indistinguishable from most other source equipment if you make a reasonable attempt to objectively find differences between them. They all get "sludged up" by the room flaws, so to speak.
If you are unwilling to treat your listening space, I wouldn't bother breaking the bank in hopes of getting significant improvements in sound performance. Concentrate more on things like component size (to best fit your available space), looks, budget and feature set, as you probably won't find a whole heck of a lot of difference in sound between them.
I've owned four different receivers, an HK 330, a Cambridge 540, an Onkyo 502 and this Panny 55 (sorry, I'm not providing the complete model numbers on these, but you all probably have a good idea of which ones I am talking about). Each time, I thought I heard SOME difference between them, but to be perfectly frank, I have no idea if that was expectation effect, confirmation bias, unmatched levels during comparisons, etc. Even when I heard differences, and I did a bit, my room is untreated and echoes and room nodes up a storm with bouncy bass waves varying like crazy depending upon the listening position. I don't trust my own opinions.
For now, the Panny 55 is good enough. It's compact and cheap.. the main reasons I've kept it over the other models I've had. I'd like to say that I think this receiver sounds much better than it's price would indicate, but I can't really.. I just take a measure of comfort from living off of the "reputational glow" which many others have bestowed upon the Panasonic family of digital receivers, in addition to my primary pragmatic requirements.
Now.. once I finally get going on incorporating room treatments, the experience of others seems to suggest that things like amps and cd/sacd players, etc., will begin to reveal their quality differences. Or, I still might not hear much of any difference at all. time will tell.