The DAC I/V board on the Marantz is also well designed. It does use a slow slew rate op amp for I/V, but it has massive amounts of local power supply caps to keep the voltage clean and smooth.
Another thing to consider is that Marantz has a HUGE retail distribution / seller network for these devices. They would sell something like 10,000 units, where the McIntosh might sell 200-300 units in comparison, so the retail price is a lot less because they can re-coup the R&D and manufacturing costs better. I’m not saying that this would equal the McIntosh or even something like Krell Foundation, but you are getting more per dollar on the Marantz than you would on the McIntosh or Krell.
I have done an enormous amount of R&D and testing with a large variety of op amps, including the best of the mix (opa627, opa827, ad797). While they can be excellent is a lot of ways, they are all compromised in one fashion or another when compared to the discrete op amps (Sparkos, Burson, Sonic Imagery). So, the discrete analog stages of the Marantz are extremely good for a processor offering at that price point, but like I said, Marantz is voiced warm so you will not have the high frequency resolution and excitement that other devices may give you (which possibly includes the McIntosh MX135).
Just keeping things in perspective.