64 Audio Nio VS Sennheiser IE900

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The 64 Audio Nio enters as the most affordable set in this lineup at $1,700, a hybrid with 1DD + 8BA and swappable apex modules. Its core tonality is warm and a touch laid-back, with the M15 module pushing bass toward “too much of a good thing”—thick, soupy, and less resolving. Swapping to the M10 cleans things up: bass settles closer to neutral, top-end clarity improves, and the presentation feels more balanced overall. Detail is respectable rather than showy, and while the Nio can be bassy, it doesn’t deliver the most controlled low end when boosted. The standout trait here is timbre—the most natural-sounding of the group, especially with M10 installed.

Used as a daily driver, Nio with M10 suits listeners who want a smooth, natural tonality without treble bite; with M15, it veers into warm-thick territory at the cost of separation and perceived detail. Against 64 Audio’s own stable, it doesn’t reach the U12t’s BA bass quality or the Trio’s stage depth, but it offers an easygoing, organic listen that some will prefer on timbre alone. Verdict: 4/5 with the M10 module; drop to 3/5 on the M15 due to excessive bass and haze.

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The 64 Audio Nio is a hybrid with 1DD + 8BA that leans into a richer, warmer presentation, trading ultimate microdetail for slam and engagement. Build and comfort are solid with a classy case upgrade; fit can vary, but tip selection helps. Technicals are mixed: imaging and separation are clean, staging is a bit intimate, and treble resolution is good via the TIA driver without sounding sharp.

The headline feature is the swappable apex modules. M15/M20 push the Nio into basshead territory—big sub-bass, head-nodding punch—while MX reins in the low end for a more balanced tonality that suits acoustic, jazz, and classical. Treble is well-extended yet relaxed; with the right tips, the 5 kHz energy avoids harshness, keeping the overall tuning smooth and non-fatiguing.

Against peers, the Nio’s strengths are its dynamics and configurable bass; its weaknesses are detail retrieval and stage size versus benchmarks like the 64 Audio U12t. Listeners chasing maximum clarity and air may prefer U12t, while those wanting hybrid physicality and tunable low-end will find strong value here. Verdict: choose M15/M20 for guilty-pleasure thump, choose MX for balance—the Nio remains a versatile, engaging high-end option.

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Sennheiser’s IE900 delivers a sub-bass–focused tuning with tight control and real tactility, but its trademark upper-mid recession (≈2–5 kHz) keeps vocals and instruments a step back. A pronounced 9–10 kHz lift adds sparkle and air; depending on tolerance, that energy can read either engaging or a touch sharp/sibilant. Technical chops are strong for a single DD—resolution and microdetail are genuinely competitive.

The sticking point is tonal balance and value. While the IE900 is refined and punchy, that blunted midrange character contrasts with its bright treble, creating a love-it-or-leave-it “blue cheese” appeal. Against peers—and especially Sennheiser’s own IE600, which fixes the mids while preserving similar resolution—the IE900’s $1,300 price starts to look tough.

In short: choose the IE900 for its clean sub-bass slam, crisp transients, and airy top if that treble profile hits the spot. If the priority is natural mids and better value without giving up much technical ability, the IE600 feels like the smarter pick—and the real redemption of Sennheiser’s IEM line.