Too many engineers and not enough marketeers on this board! The goal of a marketing brochure is not to convey data and facts but a message. It is loosely tied to facts and should never be parsed literally.
That product page linked above is a very good example of marketeering. And a fine example of how to position a product. Especially an amp which is a commoditized product. The messaging is this:
NAD has moved away from the old fashioned and very power-hungry linear power supplies and Class AB output stages that waste nearly half of the energy consumed, producing heat rather than sound. Instead, the company has developed even better performing circuits based on switch mode power supplies and Class D output stages.
NAD is differentiating this from traditional amps (including their own earlier ones) as more efficient, green, etc. Feature-wise, this is no different from a Parasound, for example.
In addition, they are also aware that there will be other manufacturers coming to market in the future with Purifi modules and they need to differentiate from them. Otherwise, they will not have the pricing power. It is like Nvidia-based video graphics card manufacturers differentiating between each other. This is the main problem in going to this type of integration with out-sourced modules.
For the latter, they cannot afford to be seen as slapping on a third party module that anyone can do as well even if it is literally true. So:
1. Use Purifi technology rather than module as much as possible. It is as generic as saying we use solar technology (rather than saying we use solar panels made by Acme inc).
2. Use statements that imply more than what it may be while plausibly justifiable i.e., your engineering having adopted it and made it better
The Eigentakt modules are manufactured by NAD under license from Purifi, allowing NAD to optimise these specifically in combination with the custom designed power supply and input stages of the C 298.
A bit of dissembling but with plausible deniability. Careful to use Purifi amplifier technology and Eigentakt modules, in this brochure. Better than using "Purifi amplifier modules" which might be used by others that aren't as market savvy.
The "input stages" could mean anything from input connectors to the input buffer. Their own input buffers can be stretched to be part of the "Eigentakt module". It doesn't say it optimizes the amp module itself but gives that impression.
This does not mean they did not manufacture the amp modules themselves but it does not necessarily imply they did either even if to tech-nerds here looking at the "green PCB" that it seems like an untruth. Their market segment is not people looking at PCB board colors inside.