ASUS managed to produce yet another interesting and well-performing DAC/amp solution. Compared to the Essence One, it is cheaper, has roughly the same features, and is insanely detailed. As an added bonus, the STU is quite small compared to other desktop DAC/amps, which is a huge advantage in our book. The sound quality per volume and its price are right at the top with the STU, making it somewhat of a bargain despite its €250 price tag.

The integrated headphone amplifier is based on the same TI chip as in the STX and other ASUS products. It is definitely a winner for medium- to high-impedance headphones. It simply sounds great and is immensely detailed. That said, it is definitely not a design well-suited to driving very low-impedance headphone and in-ears due to the STU's high output impedance and gain. Its current 2.5x and 8x gain options produce way too much volume with the dial even all the way down, making it useless for in-ears.

The STU is a step up from the STX sound card, and its headphone out seems clearer with the headphones we used for testing. ASUS definitely manages to bridge the gap between the STX and the Xonar Essence One, which is neat for all of us wanting an upgrade without having to shell out close to $600.