See the review at Audioholics...
The Marantz AV 10 15.4CH 8K AV Processor produced excellent bench test results. This $7K AVP has bass management features no other competitor has at this price. We thoroughly test to show you how it works.
www.audioholics.com
Yes it performs exceptionally well in stereo...
The most important benefit a device like the AV10 brings to the table, is the Room EQ/Treatment provided by Dirac - this has a more substantial impact on sound quality, than the DACs or Amps...
For it to process the sound with Dirac, it requires a Digital signal - if you use an external DAC and feed it with analogue, the AV10 will pass it through its own ADC, convert it to digital, before processing it and putting it out its own DAC. - This is 2 additional processing steps, with associated sound degradation along the way (whether those steps are above the audibility threshold is a different question!)
Best results are therefore achieved via feeding the AV10 directly from your source, and letting it do the DAC work alongside it doing the room processing.