Who is that other reviewer? General statements about using 2 vs 8 channel dacs, that 2 ch is better, would make no sense ("would" because I don't know what's been said about it). The reference class flagship ES9038Pro is also a 8 channel DAC. Going by the specs, the PCM1690, if implemented well should do better or at least as good as the PCM5102A. In terms of price, yes, I hear you the first time and I have been saying the same since the rumor about the use of PCM5102A, that D+M wouldn't do such as thing, but they did, proving me wrong.
Someone, forgot who, suggested may be they got the "binned" pieces, if so that's good news but realistically, reaching SINAD of 96 dB is fantastic but why not go with those that offers much higher SINAD such as 100 dB typical in the first place? Again, I am not one who believe in a 100 dB SINAD chip will sound better than a 93 dB SINAD one. Audible or not, I just prefer the best possible spec at a given price point. Overall, I would have no regret if I had bought a AVR-X4800H or Marantz C40. My only counter point to yours is only about the 1690 vs the 5102A, that on paper, one doesn't seem better than the other, for the application. By the way, the Denon AVR-X5200W, measured by Gene on Audioholics, had excellent measurements and Denon/Marantz were using the PCM1690 at the time.
We may never know why D+M picked that chip went that route despite the potentially higher cost to them. If I were to guess, as I said before, perhaps they got a deal from TI that they could not refused, keep in the mind those PCM5100 series chips have been around for a very long time.