I don't think changing receivers will make much difference re: taming the highs. IMO the "some receivers sound brighter than others" is a red herring -- although I do think a really good amplifier stage can make a difference in tighter, more solid bass in some cases which probably makes the overall sound seem a tiny bit less bright.
I hate to say this, but leaving the 7300's box and packing foam around the room would probably make more difference
BTW, I'm not saying that the 7300 wouldn't be an improvement, just that I don't think it would improve that specific issue.
