I can not recommend the STX for the K702. If you're going o use the STX with the K702 then you'll be disappointed because the STX's amp really isn't that good.
The Auditor does not sound cold or dead. It sounds like what ever you feed it. If you source is cold then the sound will be cold. It the source is warm then the sound is warm. IMO the Auditor does a good job but not as good as the Violectric V200.
The Violectric V200 is a warmer amp that has a more tube like sound. IMO that sounds works in the favor of the K702. It helps flesh out the mids, fill in the bass, and tame the highs. The K702 still remains incredibly detailed but now is much more balanced sounding.