Overview

The SMSL SU-X is a flagship balanced desktop DAC introduced in 2024. It uses dual ESS ES9039MSPRO in an 8-channel mono configuration and an XMOS XU-316 USB interface. Connectivity is comprehensive: USB, optical, coaxial, AES/EBU, and I2S digital inputs, Bluetooth (Qualcomm; LDAC up to 24-bit/96 kHz plus aptX/HD, AAC, SBC), and balanced XLR / unbalanced RCA outputs. SMSL cites THD+N 0.00004% (-128 dB), CK-03 clock processing, and a second PLL with two independent linear power supplies for digital/analog sections [1].

Scientific Validity

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As of the review date, independent third-party bench measurements of SU-X are not yet available. Manufacturer specifications indicate audibly transparent performance (THD+N 0.00004% (-128 dB); PCM up to 32-bit/768 kHz; DSD512) [1]. These are catalog specs; we treat them as provisional until verified by trusted measurement labs. No claims beyond transparency are made.

Technology Level

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Dual ES9039MSPRO with channel summing, XU-316 USB, CK-03 clocking and 2nd-stage PLL, I2S and AES/EBU inputs, LDAC-capable Bluetooth, and dual linear power supplies reflect a modern, technically ambitious implementation that goes beyond baseline DAC designs [1][2].

Cost-Performance

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Comparator: SMSL DO200 MKII — chosen because it offers balanced XLR/RCA outputs; USB/optical/coaxial/AES/EBU/I2S** inputs; Bluetooth with LDAC; and transparent measured performance reported by Audio Science Review. Its feature set is equivalent from a user perspective, and published measurements indicate transparency at ~120 dB-class SINAD (balanced) [3][4][5].

• Prices used (representative, non-sale): SU-X 999 USD [2]; DO200 MKII 469 USD [4].
• Calculation (policy formula): CP = min(1.0, 469 USD ÷ 999 USD) = 0.469 → 0.5.

Equivalence note (minimal requirement): DO200 MKII is equipped with balanced outputs and USB/optical/coax/AES/I2S, and its SINAD and dynamic range are at transparent levels, so functions and audible performance are equivalent for users [3][4][5].

Reliability & Support

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Typical warranty coverage is 1 year via authorized dealers; return/after-sales terms depend on the retailer [6][7]. Build quality appears solid, but reports note the unit runs warm under load, typical for dual-DAC linear-supply designs [2]. With standard warranty length and no systemic reliability data, we keep the score neutral.

Rationality of Design Philosophy

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The design prioritizes measurable transparency using robust clocking and power. That is rational. However, given that audibly transparent DACs with the same user-facing functions are available for roughly half the price, the SU-X’s premium mainly buys construction/feature polish rather than clearly audible improvements.

Advice

If you specifically need I2S and AES/EBU, LDAC Bluetooth, balanced outputs, and prefer the SU-X form factor or matching SH-X stack, the SU-X will satisfy. If you prioritize objective value at transparent performance, SMSL DO200 MKII achieves equivalent user-facing functionality and transparency for 469 USD, yielding a much higher performance-per-dollar [4][5].

References

[1] SMSL — “SU-X” (official product page). Accessed Aug 2025. https://www.smsl-audio.com/portal/product/detail/id/879.html
[2] Headphonesty — “SMSL SU-X Review”, updated Feb 9, 2024 (feature details, BT 5.1, usability). Accessed Aug 2025. https://www.headphonesty.com/2024/02/smsl-su-x-review/
[3] SMSL — “DO200 MKII” (official product page; feature set, inputs incl. AES/EBU, Bluetooth LDAC). Accessed Aug 2025. https://smsl-audio.com/portal/product/detail/id/721.html
[4] Amazon US — “SMSL DO200 MKII” (current market price reference). Accessed Aug 2025. https://www.amazon.com/dp/B0BFHD1RF4
[5] Audio Science Review — “SMSL DO200 MKII DAC Review” (thread with measurement plots/discussion; transparent-class SINAD). Accessed Aug 2025. https://www.audiosciencereview.com/forum/index.php?threads/smsl-do200-mkii-dac-review.41396/
[6] SMSL (Parts Express PDF) — “S.M.S.L Manufacturer Warranty” (1-year warranty). Accessed Aug 2025. https://www.parts-express.com/pedocs/warranty/SMSL%20Manufacturer%20Warranty.pdf
[7] SHENZHENAUDIO — “Guarantees & Return Policy” (retailer warranty/returns overview). Accessed Aug 2025. https://shenzhenaudio.com/pages/guarantees-return-policy

(2025.8.28)