Overview

The Monoprice Monolith THX 24459 Desktop Balanced Headphone Amplifier and DAC was a feature-rich desktop audio solution incorporating THX’s patented AAA (Achromatic Audio Amplifier) technology with dual AKM4493 DACs. Originally sold at 479 USD as part of Monoprice’s premium Monolith line, the unit combined comprehensive digital inputs, advanced DSP processing including 5-band parametric EQ, and Dirac Sensaround II headphone processing. The product has been discontinued and replaced by the Monolith 43862 model featuring ESS SABRE DACs and updated Dirac Virtuo processing at 599 USD, making the original 24459 only available through secondary markets.

Scientific Validity

Audio Science Review measurements demonstrate the THX 24459 achieves a SINAD of 107 dB, placing it well above the 80 dB transparent threshold for DAC/amplifiers [1]. Second harmonic distortion measures -120 dB, significantly exceeding transparent levels. SoundStage measurements show output power of 1420mW at 32 ohms (0.5% THD) and 183mW at 250 ohms [2]. Digital audio support includes 768kHz PCM and DSD128 capability. However, user reports confirm audible noise issues with sensitive IEMs, representing a performance limitation that affects compatibility with low-impedance, high-sensitivity loads [1]. While the unit achieves transparent levels for most headphones, the noise floor issue prevents universal transparent operation across all intended use cases, placing performance in the borderline transparent category rather than problematic level.

Technology Level

The THX 24459 demonstrates substantial technological sophistication through multiple advanced implementations. It incorporates THX’s patented AAA technology with feed-forward error correction topology, representing genuine proprietary innovation. The dual AKM4493 DAC and dual THX AAA-788 amplifier module configuration indicates significant in-house design work. Advanced integration includes comprehensive DSP functionality, parametric EQ, multiple digital filters, and Dirac processing beyond basic analog amplification. The balanced signal path throughout and complex menu-driven control system demonstrates high technical expertise. THX AAA technology has gained industry adoption, validating the approach’s technical merit.

Cost-Performance

The Monolith THX 24459 was originally priced at 479 USD [4]. For comparison, the current cheapest equivalent-or-better product with similar desktop DAC/amplifier capabilities, balanced outputs, and comprehensive connectivity is the Topping DX7 Pro+ at approximately 380 USD [6]. The DX7 Pro+ provides equivalent balanced headphone and line outputs, superior measured performance (SINAD 123 dB, THD+N 0.0001%), and comprehensive digital connectivity including USB, coaxial, optical, and AES inputs. While the DX7 Pro+ lacks the integrated DSP functionality of the original 24459, it provides equivalent-or-better measured performance and connectivity for desktop audio applications. CP = 380 USD ÷ 479 USD = 0.8.

Reliability & Support

Monolith products carry a minimum 3-year warranty, exceeding the standard 2-year average [5]. Monoprice provides global support infrastructure with established RMA processes and extended support periods beyond typical consumer electronics. The complex digital/analog hybrid design with sophisticated DSP processing represents average reliability risk compared to simpler analog designs. Customer experiences show generally responsive support, though some inconsistencies in service quality have been reported. The established Monolith brand under Monoprice demonstrates a positive reliability track record in the audio market.

Rationality of Design Philosophy

The design philosophy demonstrates rational scientific approach through multiple evidence-based decisions. The incorporation of THX AAA technology represents measurement-focused improvement with documented distortion reduction benefits verified through independent testing. The comprehensive DSP integration including parametric EQ and Dirac processing addresses scientifically-valid acoustic correction requirements. Digital signal processing and software-based audio enhancement align with contemporary rational approaches to audio improvement. The all-in-one integration philosophy reduces external component requirements and potential interface issues. While the product commanded premium pricing, the technical approach prioritized measurable performance improvements and functional integration over subjective audio mythology. The discontinuation in favor of updated ESS DAC technology demonstrates progressive adoption of improved components rather than attachment to outdated designs.

Advice

The Monolith THX 24459 is no longer available for purchase as it has been discontinued by Monoprice. Users seeking equivalent desktop DAC/amplifier functionality should consider the Topping DX7 Pro+ at 380 USD, which provides equivalent balanced outputs and superior measured performance. For desktop applications requiring integrated DSP functionality, the replacement Monolith 43862 at 599 USD offers updated ESS SABRE DACs and Dirac Virtuo processing. Cost-conscious users prioritizing pure audio performance can choose the JDS Atom stack at 258 USD for superior measured performance without integrated DSP, supplemented by software EQ solutions. The Topping DX7 Pro+ represents the most cost-effective path to equivalent desktop DAC/amplifier functionality, while the Monolith 43862 provides the closest direct replacement experience with DSP features at significantly higher cost.

References

[1] Audio Science Review - Review and Measurements of Monoprice THX Desktop DAC & Amp, https://www.audiosciencereview.com/forum/index.php?threads/review-and-measurements-of-monoprice-thx-desktop-dac-amp.7483/, accessed 2025-09-25

[2] SoundStage Solo - Monoprice Monolith THX 24459 Desktop Balanced Headphone Amplifier and DAC Review, https://www.soundstagesolo.com/index.php/equipment/amplifiers/195-monoprice-monolith-thx-24459-desktop-balanced-headphone-amplifier-and-dac, accessed 2025-09-25

[3] JDS Labs Official - Atom DAC+ and Atom Amp+ Specifications, https://jdslabs.com/product/atom-dac/, accessed 2025-09-25

[4] Monoprice Official Product Page - Monolith 43862 Desktop Balanced Headphone Amplifier and DAC, https://www.monoprice.com/product?p_id=43862, accessed 2025-09-25

[5] Monoprice Warranty Policy - Official Support, https://monopricesupport.kayako.com/article/263-monoprice-warranty, accessed 2025-09-25

[6] Topping DX7 Pro+ Desktop DAC/Headphone Amplifier - Official Product Page, https://www.toppingaudio.com/featured/topping-dx7-pro-review-their-best-all-in-one-yet, accessed 2025-09-25

(2025.9.26)