I have the WA22 & it seems to drive the HE-6 well & then I tried them on my Tube Speaker Amp.
It sounds more dynamic with better quality Bass (depth & texture) also I can hear more details & Sound stage has more depth. But this comparison is from memory, I haven't heard the HE 6 with WA22 after I tried them on the speaker amp. Today I will do a direct side by side A/B comparison between the 2 & reconfirm whether my above impression based on auditory memory is correct .
Above confirmed after A/B comparison, except the sound stage , it seems nearly the same on the WA22. WA22 highs are a bit shrill whereas the Cayin highs are smoother, overall sound has more weight, is more fleshed out. Amongst the frequency range the Bass has the most improvement (but perhaps I give that the most importance as I am a bass-head).
The WA22 has good NOS tubes (cost around $ 800), whereas the Cayin has stock current production average tubes ( around $ 120). Have ordered some nice NOS tubes, so will expect some more improvement.