I bought a 501 on line and it works fine. Today I found a 595 at a yard sale for $35 and was wondering how they compare. I want to give the not quite as good one to a friend.
So far I have noted Onkyo's rating of 65 watts RMS 6 channel for the 501 and 75 watts RMS 5 channel for the 595.
The 595 only does 5.1 while the 501 does 6.1 - not a big deal for me either way at this point.
My guess is that 10 watts RMS per channel won't make a big difference on my speakers.
The 595 also does not list a crossover to sub level. Because it lets the sub handle it and does not mess with it? The 501 has an adjustable crossover frequency level.
I guess I should explain - I don't trust my ears for one or two listens. Over a few months I would know which was better, but it seems on any given day I can get pretty subjective.
Also, maybe one day I would realize that the subwoofer cross over or some other feature is really needed and would kick myself for giving away the wrong receiver.