One is also comparing an s/s DAC to a balanced s/s out compared to a s/s DAC to a tube s/e out... But since you asked, the NFB10 out holds its own Balanced. With the ES chip and increased gain (x4 according to Kingwa over s/e) it pulls the details out and separates the instruments. This works well with the HE-500, but makes the HE-6 prone to a hotter high end.
Between you and me, what I tried with the HE-6 was to set the NFB-10 to high gain and feed that signal into the EF-5 also on high gain. It was sweet.
Really? I don't find the NFB-10ES + HE-6 setup too bright...a bit on the bright side but nothing unpleasant