The Acoustic Research M2 is probably the best thing we've ever had pumping music into our earholes.
There's a depth and clarity, a broad separation and a real sense of power and purpose behind the way the M2 delivers its audio experience. With a pair of quality headphones, like the OPPO PM-3s, you get a stunning level of sound quality.
That Class A amplifier enables the M2 to drive audiophile headphones with genuine power, something the cheaper Pioneer XDP-100R seriously lacks.
But while the AR-M2 is capable of delivering an almost transformative audio experience with the hardware and software at its disposal, that doesn't necessarily make it the be-all-and-end-all of portable music devices.
It sounds great, but it's by no means the perfect player.
The Android Jelly Bean OS is very much last-gen software, and the lack of access to the full Google Play Store does limit the M2's usability on that front. You can get a decent suite of audio apps installed, such as Spotify and Tidal, but it's all via the side door – you have to download the .apk files separately and side-load them onto your device.
It's a terribly clunky way to roll in these modern times.
And adding other playback apps to the device can seriously confuse it too. We've had instances where we've been playing a track using the AR Music Player, paused using the physical controls down the right-hand side, and then when we hit play it continued the last tune we'd been playing from the Tidal app.
Acoustic Research is still keeping the software updated – it's recently brought in gapless playback for its high-res audio app – but you're unlikely to see any Marshmallows adorning the M2.
Having those physical controls is a great bonus for the player, meaning there's no need to turn the screen on to skip, play or rewind tracks, but because they sit so far proud of the chassis they're very easy to press by accident when pulling the M2 from your pocket.
The analogue volume control is similarly easy to nudge in the pocket. In one direction that's slightly annoying but not a huge problem; in the other the power of the M2 means you can end up really battering your eardrums.
Battery life is a bit of a struggle for the M2. It may have that 4,200mAh battery, but the powerful amp really does demand a lot from it, and as such you'll be lucky to hit the nine hours of audio playback AR promises; it needs a fair while to charge back up too.
It really is all about the audio when it comes to the Acoustic Research M2. All other considerations were obviously secondary when it came to designing this audiophile portable player – which is quite a refreshing stance.
And, given the quality of sound you get out of it with a pair of good headphones, AR's single-mindedness is almost entirely justified. Going back to my phone, or even another high-res player, after the M2 is an aurally disappointing experience.
The bountiful internal storage is impressive, as are the microSD and OTG USB expansion facilities, and the supreme power of its output doubly so.
It's really not the most user-friendly of players. The Android OS is familiar, but the necessary side-loading of audio apps is a frustration. And while the AR Music Player, with its own lossless audio path, delivers great sound, it's not a particularly attractive or intuitive application.
Then there are the easily-pressed-in-error physical buttons. They sit far too proud from the metal chassis, as does the analogue volume control, which we often found got nudged when we dropped it into a coat pocket.
The battery life is a touch lightweight too, mostly thanks to that behemoth of an amplifier chewing through the beefy 4,200mAh battery. The device itself though is definitely not lightweight, and has a serious heft to it.
As much as the Acoustic Research M2 is probably the best-sounding device I've ever plugged headphones into, there are some definite issues which stop me from giving it a resounding recommendation.
Obviously the price is pretty staggering, but then there is a wealth of high-quality componentry inside the M2.
I love the sound, but throughout my time with the M2 I kept finding myself going back to the Pioneer XDP-100R. It doesn't sound as good, but it's a more long-lived, more versatile and more convenient device.
The M2, though, is all about the audio – and if you are too then you'd have to look long and hard to find another device which sounds this good.