I've been using an Aune S16 as my Primary DAC in my listening station for well over a year now. It is a fantastic DAC very musical, detailed, with a dead silent noise floor. It is every bit as good as my Chord Mojo and in some ways better. The one negative issue I've experienced is a rather annoying transient pop when the unit switches from DSD content back to PCM. This pop does not occur when starting DSD content only when it switches back to PCM from DSD. If you have the volume up loud it can be rather jaring and I've sometimes worried about possible damage to certain headphones however no headphones I've used have been adversely effected so far. I generally try to remember to turn the volume down when I know I'm switching to non DSD source material.
The headphone amp section of the S16 is merely adequate in my experience. The volume knob has to be cranked up to the 70%+ point to power more demanding cans. It's sound is okay but nowhere nearly as good as either the H10 or Crack. I've not heard the WA22 but knowing how well the Crack combines with the s16 I can't imagine the Woo/S16 pairing being anything other than excellent to fantastic.
I generally run the balanced out to a Gustard H10 and the RCA outs to my Bottlehead Crack. The S16 is nice paired with either amp especially when using the H10 for orthodynamics and the Bottlehead with Senn HD6xx series or Beyer T90. If you don't mind dealing with the DSD to PCM pop or don't mess with DSD the S16 is hard to beat if you can get one for no more than $550 or so. (Amazon has 2 at $499 as I type this) At the full retail price of $699 you are getting into lots stiffer competition in the DAC world.
I've not found much information regarding the S6 however if the S16 is any indication it's very likely that it too will be one of Aune's better products. I'm not sure that the S6 is positioned to be a higher end product than the S16 however it appears that the S6 has replaced the S16 on Aune's own website. I would assume the S16 is now discontinued since it has been deleted from their products section. Also, I get the feeling that the S6 is really a lateral update to their flagship dac/headphone amp. The S6 has the slightly higher specced AKM DAC chip and I've not seen any confirmation that it uses the same or better Crystek clock chips that are present in the S16. I credit much of the Aune's superior performance due to these extremely precise and rather expensive USA made clock chips.
BTW.. My full signal chain: Windows 10 PC > Schiit Wyrd > Gustard U12 USB Interface > S16 via AES/EBU input > Gustard H10 or Bottlehead Crack. I think using the U12's AES/EBU output into the S16 improves overall smoothness and resolution by just a bit over Wyrd directly into the S16's own USB.
If you decide to go with either Aune it would be nice to hear your thoughts regarding performance with the Woo.