Ok, I dug this up again and here is what I found:
1. 659 is rated 100wpc while 661 is 90wpc (all other things being the same)
2. 659 supports HDMI 1.1; 661 does HDMI 1.2a -> I'm not sure this is of any major consequence to me except possibly something to do with data from SACD not having to be decoded in the player but rather directly in the AVR.
3. 659 does not do HDMI repeating (or switching or whatever); 661 does
4. Something to do with Simplay -> 661 has it; 659 does not (if this statement makes any sense at all).
So can someone tell me what Simplay is? I'm sure I don't really care, but just out of curiosity. Going to Simplay's site brings up a lot of marketing hogwash that I'd rather not go through if someone who already knows can shed some light.
Other than that, just killing time here..

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