When Astell&Kern and 64 Audio announced they were teaming up, audiophiles took notice. Now, months after its initial teaser at High End Munich, their first joint creation is here: the XIO. It’s a $3,000 pair of in-ear monitors (IEMs) that brings together the hardware expertise of Astell&Kern with 64 Audio’s know-how in multi-driver earphones. This isn’t your average pair of earbuds—and it’s not meant to be.

That price tag isn’t just about brand names. The XIO brings together some of the most complex engineering either company has put into an IEM—combining ten drivers per ear, a highly customizable sound profile, and materials you usually find in luxury watches, not earbuds.

Let’s start with the internals. Each earbud in the XIO packs a ten-driver hybrid system. That’s a lot, even by audiophile standards. Here’s how it breaks down:

• Two dynamic bass drivers share a sealed chamber, designed to deliver deeper low-end impact.
• Six balanced armature drivers cover the midrange.
• Another armature handles the upper mids.
• And a high-frequency driver—placed right at the end, without a sound tube—tackles treble.

That high-frequency setup is worth noting. Most IEMs use small tubes to funnel sound from the driver into your ears. XIO ditches that with what’s called a “direct-radiating” design, which can reduce distortion and give treble more room to breathe.

To keep all these drivers playing nicely together, the XIO uses a four-way passive crossover. That’s basically an internal traffic director, making sure each driver gets just the part of the audio spectrum it’s built to handle. The result is a claimed frequency range of 5Hz to 22kHz—covering everything from sub-bass rumbles to detailed treble sparkle.

Beyond just driver count, the XIO includes three pieces of patented 64 Audio tech designed to improve sound and comfort:

• tia (Tubeless In-Ear Audio): This replaces traditional sound tubes with a single-bore design to reduce resonance. The goal? Clearer, more lifelike audio.
• apex® (Air Pressure Exchange): If your ears ever felt “plugged” during long listening sessions, this venting system is meant to relieve that pressure—without sacrificing noise isolation. The XIO comes with four interchangeable apex modules that each offer different levels of isolation and openness.
• LID® (Linear Impedance Design): This tech helps keep the XIO sounding consistent no matter what you plug them into—whether it's a high-end player, a desktop DAC, or even a phone with a decent dongle.

The included apex modules (m20, m15, m12, and mX) allow listeners to tweak how much external noise gets in and how “open” the sound feels. The m15 module is exclusive to the XIO and features a stainless steel body with a black diamond-like carbon (DLC) coating.

Speaking of that DLC coating—the XIO’s shells are made from 904L stainless steel, the same metal used in some high-end wristwatches. It’s tough, corrosion-resistant, and more complicated to machine than the stainless steel found in most audio gear.

The outer faceplate is designed to reflect light in complex ways, giving it a 3D effect that fits right in with Astell&Kern’s visual style. Even though it’s an IEM, the XIO looks like a carefully sculpted object.

For a $3,000 IEM, the packaging comes loaded. Inside you’ll find:

• The XIO monitors themselves
• A high-end leather carrying case
• Three types of ear tips (foam, SpinFit silicone, and standard silicone) in three sizes each
• A silver-plated UP-OCC copper Litz cable with 4.4mm termination
• A cleaning cloth and tool
• A cable clip
• All four apex modules (each with different materials and tuning profiles)

The cable is a four-core, cross-braided design meant to shield against noise and ensure signal clarity. With an ultra-low 0.29-ohm impedance, it’s engineered to pass audio cleanly without adding resistance to the signal chain.

Let’s be real: this isn’t something you grab to listen to a podcast on your commute. The XIO is built for serious listeners—people who spend time with their music and want control over how it sounds. If you’ve invested in a quality digital audio player or desktop rig, and you’re looking for a high-end IEM to pair with it, the XIO might be on your radar.

That said, it’s a niche product. It won’t appeal to everyone, and it’s not trying to. But it does show what’s possible when two companies known for their audio chops come together on something new.

The Astell&Kern XIO goes on sale globally in August 2025 through authorized dealers.