Pro-Ject Pre Box S2 Digital Headphone Amp/DAC Review

PRICE $399

Dual mono DACs
DSD and MQA support
Can function as a preamp
Limited portability

Pro-Ject’s compact amp/DAC pairs especially well with modestly priced headphones, and it can also serve as a stereo preamp.

More people are listening to more diverse high-resolution audio formats through higher-quality headphones than ever before. But ideas about how to feed those headphones vary. The headphone amplifier/digital-to-analog converter, a popular hybrid product, is among the most tireless shape-shifters on the audio scene. I’ve reviewed Amp/DACs as compact as a USB stick and as big as a full-size rack component. At about 4 x 1.5 x 4 inches (WxHxD), Pro-Ject’s Pre Box S2 Digital falls somewhere in between. You wouldn’t carry it in a pocket, but it doesn’t take up much space on a busy desk.

Features and Setup
You might know Pro-Ject as a purveyor of affordable turntables and other phono gear. But the 27-year-old Austrian company, distributed in North America by Sumiko, also offers what it calls “box designs,” which include DACs, power amps, headphone amps, and various other devices. Pro-Ject’s European arm also offers CD and streaming players.

As its name implies, the Pre Box S2 Digital can serve as a stereo preamplifier as well as a headphone amp and DAC. Pair it with a stereo power amp or a pair of powered speakers, and you’ll have a good starter system. Up to three digital sources—USB, coaxial, and optical—can plug into the back panel. There’s no analog input or Bluetooth connectivity, however, so turntables and smartphones are out of luck.

The quarter-inch headphone jack on the Pro-Ject’s front panel suggests that this Amp/DAC is seeking to mate with full-size headphones. Also up front are a 1-inch color status display, a volume knob, and control buttons to select inputs, access the menu, and select between various digital filter options. The eight filter settings include Pro-Ject’s proprietary Optimal transient digital filter.

A small, plastic 12-button remote duplicates the front-panel controls, adding mute, balance, and transport. (A more substantial metal version is available for $79 extra.) The chassis, front panel, and even the buttons are all pale gray aluminum, giving the little box a solid feel.


Through its USB input, the Pre Box supports up to 32-bit/768kHz files in PCM formats, and DSD via PCM up to DSD512, which covers any digital file you’re likely to buy or stream (and then some). The digital coaxial and optical inputs support files with resolutions up to 24/192.

One of the Pre Box’s interesting features is MQA support—more on that later. When playing files with MQA, the display shows the MQA logo plus a blue dot in the upper right corner. MQA is supported only through the USB input; the company says implementing it through the other digital inputs would have increased the cost of parts and boosted the Pre Box’s price.

Unlike most DACs in this price range, the Pre Box features dual (ESS SABRE) DACs and separate left/right signal paths. Other differentiating features include a new proprietary clock design, ultra-low jitter, and a combination of active and passive filtering to eliminate noise from the USB output feeding the DAC.

The Pre Box can be powered directly via most USB connections. Otherwise you’ll need to use the external power supply. MQA and DSD playback require installation of a computer driver from a supplied CD-R. Otherwise, the Pro-Ject is ready to go for Windows 10 and Linux. Most Mac OSX versions are supported except for El Capitan and Sierra.

Pro-Ject Audio Systems
(510) 843-4500