A little background about the headphone stage of the PureDAC:
First of all it delivers up to 13Vrms and a current not less than any other headphone amp. There is nothing a headphone amp is delivering differently, beside of course, individual sound flavours depending on the product. In addition the PureDAC headphone part delivers the signal voltage and the signal current from separate sources phase independent! This is very unique and a significant advantage when driving headphones with strong phase shifts - in other words: dynamic headphones with a strong motor (Beyer T series, Fostex TH900, AKG...).
The fact that is doesn't need an additional amplifier to provide the above specs and also delivers a lossless volume control are an achievement and surely not a simple "add-on"!
So far almost all comparsions to the PureDAC's internal headphone stage were with clearly more expensive gear - look a John's review. Of course we are able to deliver more quality for a thousand bucks (or even more) extra. The hard part is to deliver quality in a way people can afford the product and everything else we could do in addition.
The PureDAC is the very first "DAPC" (Digital Analog Power Converter) and as a new concept it has quite some space for further improvements.
The PureAmp is already inside our latest catalogue although we expect the product earliest in September. Specifically the use of the B.M.C. link with the shared DIGM and CI operation mode will be attractive for PureDAC owners.
What we do is not just synergy between products. We are establishing new ways of component interaction, shortening the signal path significantly and reducing losses. Naturally those operation modes are incompatible to traditional standards and that's why we always also offer a compatible operation mode.
Design philosophy has to be founded on scientific research and this means to search for better ways to preserve music. But this would be a discussion that belongs to some non product specific place.
Hope this explanation provides a little insight.