I highly suspect that you would be losing sound quality if you moved from SSP-800 to an AVM 60. Sure, you would be getting the new sound formats, but I think there is a distinct difference in what's put into the analog audio stages.
You might look into the Krell foundation. With that, you would get 4K and Krell's ARES room correction. I think it may be somewhat of a lateral move in sound quality from the SSP-800 (or maybe a little bit different signature). Of course, you would not get Atmos and DTS:X. Honestly, to me, the new Atmos/DTS:X modes wouldn't really make a difference unless you had the extra speakers (such as height/ceiling). Even so (and I've said this before), I would rather have an ultra-realistic sounding 5.1 system than a decent sounding 9+ channel system. :)
If you had your heart set on Atmos and DTS:X, I would look hard at the Marantz AV8802a to get the most out of sound quality.