In this review, I take a deep dive into the Muse HiFi M6 Double portable DAC & headphone amplifier. The M6 Double features a cascading display with neon Nixie IN-17 tubes and JAN6418 tubes for amplification, alongside a flagship ESS Sabre ES9039 DAC chipset. It’s priced at $399 USD.
Disclaimer: This sample was provided by HiFiGo for an honest review. All observations and opinions here are my own, based on my experience with the product.
Muse HiFi M6 Double
Features
I previously reviewed the Muse HiFi M5 Ultra device and came away thoroughly impressed by it. So I was excited to learn about the M6 Double and even more excited to hear it for myself. This one has some new tricks up its sleeve.
One of the standout features of the Muse HiFi M6 Double is its use of double tube types (hence the “Double” in the name). It uses a pair of Nixie IN-17 cold-cathode tubes for the volume display, giving the M6 Double a unique and distinctive appearance.
Invented in 1950, Nixie tubes were widely used in aerospace controllers, vintage calculators, and even Wall Street stock displays. These tubes are now quite rare, so the M6 Double is a limited-edition model, with only 1,000 units available worldwide.
The other tubes inside the unit are dual JAN6418s. Once again, Muse HiFi has implemented a shock-absorption system to eliminate any ringing or microphonics during handling—and I’ve got to say, they’ve absolutely nailed it. You can handle the M6 Double like any normal portable device, and there’s zero ringing or unwanted noise to be heard.
Like the M5 Ultra, the Muse HiFi M6 Double includes Bluetooth connectivity. In this case, we get Bluetooth 5.2, powered by Qualcomm’s latest QCC5125 chipset, which supports high-definition codecs such as LDAC and aptX Adaptive.
Inside, the DAC section is handled by an ES9039 chip. This flagship DAC supports Hi-Res 32-bit PCM and DSD playback, ensuring top-tier digital performance. The ES9039 also comes with 7 different digital filters for fine-tuning.
A built-in 4,500mAh battery provides ample power for the unit. Although the specifications don’t list exact battery life, I found it delivers around 10 hours of normal use, whether you’re running in transistor or tube mode, wired or wireless.
The specifications don’t mention the output power of the unit but it’s enough to power all of my headphones (to be honest, I don’t have anything that’s particularly demanding or hard to drive). A three-level gain adjustment means the M6 Double is compatible with everything from sensitive in-ears to full-size headphones.
Design
The Muse HiFi M6 Double has a lovely anodised aluminium chassis with a smooth matte finish. The front and rear panels are glass, and the front panel gives you a clear view of the internal PCB and circuitry. It has a reassuring heft to it, helping it feel premium in the hand.
On the lower panel, you’ll find the 3.5mm and 4.4mm headphone outputs, along with two USB-C ports: one for data and the other for charging the battery.
The right side of the unit hosts a large volume wheel, together with the power and playback controls. On the left side are two perforated vents that reveal the glowing JAN6418 tubes and help dissipate heat.
Included in the box is a lovely green leather protective case. It fits the device snugly and leaves the volume knob and control buttons easy to access. It looks great and adds a good layer of protection to the unit.
Sound
The M6 Double sounds exactly as you’d hope from a device like this: clean, confident and surprisingly refined. In transistor mode it has a tidy, modern character with a solid low end and a nicely defined midrange. It doesn’t try to draw attention to itself; instead it presents music in a clear, stable way that lets you settle in and just enjoy what you’re hearing.
Switching to tube mode adds a gentle touch of warmth and texture. The JAN6418 tubes don’t smear the details or soften things too much, but they do bring a slightly smoother tone and a bit more “give” to vocals and acoustic instruments. It’s subtle but satisfying, and the shift is immediate, making everything sound a little more inviting.
Both modes are very good in their own right, and the ability to swap between them makes the M6 Double feel versatile without complicating anything. It’s one of those devices where you quickly find a setting that suits your mood and just let it play.
Verdict
I’m still trying to get my head around the fact that they managed to keep the price down to $399. Considering the build quality, the level of ingenuity and engineering involved, and the overall uniqueness of the product, it offers excellent value for money.
The Muse HiFi M6 Double blends nostalgia with modern design, and most importantly, it sounds fantastic in both transistor and tube modes. It is a clever, well-executed device that feels special every time you pick it up.
If you are looking for something distinctive that also performs at a high level, I can comfortably recommend the M6 Double.
