+1
The xx5 Yamaha models have left me completely unimpressed.
My choice, given the two you gave, would be the 663.
It would no doubt be less expensive and have a better amp section.
I agree with you.
* By the way Nomo, you own the Yamaha RX-V1800.
How would you like to see the guts of your receiver?
Here:
http://www.areadvd.de/hardware/2008/Yamaha_RX-V1800_01.shtml
>>> At the bottom of each page on the left side, there is some blue lettering saying "Weiter zu Seite 2", (just click on that) and up to page 5. So, all together there are 5 pages.
I know, I know, it's in German, but it's just for looking at the nice pictures.
And the final score on the 1800 is the best (Reference, full 10 stars

).
Excellent verdict ("Fazit").
Perhaps you already saw it, but anyway, let me know if you enjoyed it.
Cheers,
Bob