Synergy

Given the ZD3’s slightly warm, smooth tonal balance, I found it paired best with neutral to slightly bright amplifiers. This approach maintains detail and air while benefiting from the ZD3’s natural timbre and forgiving nature.

The Topping L30 II proved an excellent amplifier match. Its neutral, clinical-leaning character complemented the ZD3’s warmth perfectly, preserving the DAC’s smooth midrange while adding a touch of treble clarity and extension.

For headphones, the Sennheiser HD 600 worked well with the ZD3. The HD 600’s neutral tonal balance and somewhat lean bass benefited from the ZD3’s added warmth, resulting in a natural, engaging presentation with excellent vocal reproduction.

However, the ZD3 proved less ideal with warm or bass-heavy headphones like the Modhouse Argon Mk3. Pairing it with warmer, bass-emphasized cans risked making the presentation too thick and congested, with reduced clarity and treble presence.

On the IEM front, the neutral-leaning MOONDROP Blessing 3 paired exceptionally well. The Blessing 3’s slight analytical tendency was softened by the ZD3’s warmth, resulting in a balanced, musical sound that retained technical prowess while gaining emotional engagement.

Conversely, the V-shaped Yanyin Canon II proved to be a less-than-ideal match. The Canon II’s elevated bass and treble, combined with the ZD3’s mid-bass warmth and rolled-off highs, created an unbalanced presentation that emphasized impact over refinement.

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SMSL D-6S

Technical

Both the Fosi ZD3 and SMSL D-6S feature the same ESS ES9039Q2M DAC chip, supporting identical PCM decoding up to 32-bit/768kHz via USB and native DSD512 playback. This shared foundation means their basic decoding capabilities are essentially matched.

However, the D-6S includes MQA decoding and MQA-CD unfolding, features completely absent on the ZD3. For those invested in the MQA ecosystem, this may be a significant advantage.

Connectivity differs greatly. The ZD3 offers USB-B, HDMI ARC, optical, coaxial, and Bluetooth 5.0 with aptX HD, aptX, AAC, and SBC. The D-6S provides USB-C, optical, coaxial, and Bluetooth 5.1 with LDAC, aptX HD, aptX, AAC, and SBC, but notably lacks HDMI ARC input.

Both units offer balanced XLR outputs (5Vrms) and RCA outputs (2.5Vrms), matching output voltages exactly. The ZD3 includes a 12V trigger in/out for system automation, while the D-6S omits trigger functionality entirely.

Feature-wise, both include OLED displays and infrared remote controls for convenient operation. The ZD3’s display is circular and 1.5 inches, while the D-6S uses a 7-segment LED display behind frosted glass. Both provide preamp functionality with variable volume control.

The ZD3 allows user-replaceable op-amps (LME49720 stock) for sound customization, while the D-6S uses fixed OPA1612 op-amps with no user-serviceable options.

The D-6S offers adjustable digital filters and DPLL bandwidth settings accessible via its menu system, features that the ZD3 doesn’t provide.

Power handling differs significantly. The ZD3 uses a 12V DC external power adapter, while the D-6S employs an internal 100-240V AC power supply with a three-prong connection, eliminating the need for an external power brick.

Design

Both DACs embrace minimalist aesthetics with CNC-machined aluminum chassis finished in matte black anodizing. The ZD3 is slightly larger and heavier, but not enough to cause any issues, even in a desk setup

The D-6S features a frosted glass front panel that resists fingerprints better than glossy finishes, with a 7-segment LED display that becomes nearly invisible when powered off. The front panel protrudes slightly, creating a floating effect that adds visual interest.

The ZD3’s circular OLED display and orange volume knob create a more contemporary, symmetrical appearance with a stronger design personality.

However, its fully visible display means there’s always something to see, even when not actively in use. I personally found the display of the ZD3 to be much more usable than the D-6S.

Both units use volume encoder knobs that double as multifunction buttons for menu navigation and input selection.

Build quality is excellent on both, with tight tolerances and professional fit and finish. The D-6S’s slightly lighter weight makes it easier to reposition, while the ZD3’s extra heft provides marginally better stability with heavy cables.

One minor criticism of the D-6S is the sharp corners on its protruding front panel display, which can catch fingers during handling. The ZD3’s rounded edges throughout prove more comfortable to interact with.

Performance

Despite sharing the same DAC chip, the ZD3 and D-6S take different approaches to their sonic presentations.

The D-6S delivers a neutral, transparent, and highly dynamic sound signature with minimal coloration. Bass hits are tight and impactful without added warmth, maintaining excellent texture and control.

The ZD3 sounds warm and musical with enhanced mid-bass body and natural midrange timbre. Its presentation prioritizes listenability and organic character over clinical accuracy, creating a more forgiving sound with less-than-perfect recordings.

In the treble region, the D-6S provides superior extension and detail with a slight sparkle that enhances perceived resolution.

Cymbal crashes and high-frequency information are clearly articulated without introducing sibilance, maintaining smoothness while maximizing information retrieval.

The ZD3’s treble rolls off more gently, creating a relaxed, smooth top-end that avoids any hint of harshness but sacrifices some air and micro-detail.

Dynamics are a strength for both, though expressed differently. The D-6S excels at conveying the full dynamic range between the loudest and softest elements in a mix, creating an exciting, lively presentation that feels natural and engaging.