All of the boutique opamp input buffer versions that ASR has measured to date have measured less clean than Purifi's EVAL1 input buffer.
The EVAL1 measures 3dB better without pre-gain than with pre-gain so if any improvements are to be had, would be have pregain without the 3dB loss in SINAD. So far, I haven't seen anyone achieve that.
These boutique opamps appear to be expensive tone controls (which can be done elsewhere). VTV just posted a tube based input buffer version for a significant price increase (+1,250). I understand they are a tube company, but don't see the value add other than marketing.
The only possible "value add" that I have seen is a micro-controller version from Vera Audio that allows bridging of both the NC500 and Purifi modules but they aren't cheap.
https://www.vera-audio.com/newsarticle.php?news_id=3
