I had the NAD C658 for a few months, starting Nov 2019. This was because I needed a streamer solution, considered the 272, but decided it’s too outdated and I’d wait (which finally ended in not waiting and the current system). It was nice, and when things started to develop during this year, I replaced the weakest link first, which was the power amp. I tried 200, 250, and 300 with the NAD, and have to say that it grew with the amps, it was not the case that the better power amps exposed its weaknesses more. I ended up with the 300, the idea being that this would set the level and I could live with the NAD until the 272-2/372.
Feature-wise it was nice, especially for the price. @popeye, while both Roon’s solution and Dirac are categorized under DSP, they are not really comparable. The NAD comes with a microphone for room measurements and the Dirac system performs impulse correction.
The sound with Dirac was interesting and I do think beneficial in a hifi way, but it was also rather tame. In part this depends on the frequency correction curve that you apply, but it did not feel very “musical” in the Naim sense. It’s also a bit of faff to set up, and only after you have done it do you start to realize how much the room changes all the time.
The NAD then contributed to the current system by starting to fail in January, it randomly made high-pitched sounds. This seemed to only occur when Dirac was enabled. I lived with it through the first lockdown, then sent it to service, from which it never returned. After several months and inquiries, the NAD distributer told my dealer that there were supply problems due to the pandemic, and other manufacturers were also affected - I suppose some kind of chip. So the dealer took back the NAD and I bought the 252/SC/NDX2/555 instead right away instead of waiting for the 272-2.
All in all, I’d say it’s a capable piece of kit, especially wrt features at the price, and can sound better than you’d expect. It does not hold a candle to the 252/NDX2 of course, but why would it.
And @litemotiv, when you compare the price for Roon and the NAD, you can of course only compare for the multiroom features. Roon is so much more, but of course it depends on whether you need what it does