TechPowerUp posted a review on the ASUS Xonar Essence STU DAC/Amp
A quote from the article:
ASUS's most recent DAC/amp gets put to the test. This time, the Xonar Essence One gets a new little brother in the Essence STU. The new STU is a sleek-looking, small foot-print DAC/amp with excellent specs. We put it to the test to see how it measures up to other similar solutions!ASUS Xonar Essence STU DAC/Amp @ techPowerUp