I have four avrs in the house. They're far more similar, aside from dsp/connectivity/feature set, than different sq-wise. Hard for me to appreciate your observation. I think you're expecting too much, from your comment like "blow the doors off" because it's newer. I have old 2ch separates (more than one set, too) and they don't have any particular advantage over the avr sq wise and don't approach them in usefulness.
There's a lot of folk who seem to get all excited about old receivers, I'm not one of them (and if I'd hung onto my old 2ch Marantz could sell it more today than I paid for it it seems, crosstalk and all), and don't think separates for multi-ch are worth the extra cost. Three of the four I've got can act as pre-amp and they do that quite well when I've added amps. Some like tube amps, don't care for using those either. YMMV.