First impression: the Aurender Flow looks and feels like a high-end component. The impeccably finished solid aluminum case, big volume control knob, and all-metal control buttons let you know this is the real deal. As for sound quality, it's spectacular!
Connectivity is limited to just oneport and an optical digital input, plus a 6.3mm headphone jack. Flow handles up to 192 kHz/24-bit digital files via the optical connection (more about that later), and ultra-high resolution 384kHz/32-bit and DSD128 files via USB. There are no analog inputs.
Measuring 3.1 x 5.4 x 1.1 inches (80 x 137 x 28mm) and weighing one pound (450 grams), the Flow is a little too big to stuff in your pocket. I used it mostly as a desktop digital converter/headphone amp; some Flow owners might take it to work, or on long flights. The Flow comes with a handsome leather carrying case.
The big volume control makes it easy to get to exactly the volume I want with a flick of the wrist. The 4,450mAh battery's play time tops out at 7 hours; at home you can charge the battery as you listen. If you own a large library of music, you can take a lot of it with you by installing an mSATA drive (up to a 1TB) inside the Flow. (The Flow is a digital converter/headphone amp, not a music player like an Astell & Kern or Pono.)
Since the Flow sports a 6.3mm headphone jack, I started listening with my AKG K812 full-size headphones. The sound was sweet, highly detailed, massively spacious, and the midrange tonality was oh-so natural. I immediately settled down and just relished the sound. When I'm writing a review, I'm usually comparing one product to another, but this time I just wanted to take it all in. The Flow was that good!
Most of the time I played the Flow hooked up to my Mac mini, but I also listened with my Oppo BDP-105 Blu-ray player, via the Flow's optical input. While the Flow is supposed to play up to 192 kHz/24-bit files, it didn't, though 96 kHz/24-bit files were no problem. So I checked with Aurender's Division Director Harry Lee, and he confirmed there were compatibility issues for 192 kHz/24-bit files via the optical input with some players. However, the 96 kHz/24-bit files sounded great.
I spent most of the time listening to standard-resolution Apple Lossless and FLAC files. After all, most potential buyers will own a lot more standard-resolution files than high-resolution ones. The sound feels incredibly precise, but never cold or overly analytical. The new Audeze EL-8 headphone's clarity was excellent while listening to streaming FLAC files from .
My Shure SE846 in-ear headphones sounded faster, more dynamic and open with the Flow than any other amp I've tried. The Centrance Hi-Fi M8 amp had a leaner presentation; the Flow had a fuller, richer balance, which I preferred. The Flow had no problem driving my very high-impedance (600 Ohm)headphones.
I wish I still had the Chord Hugo portable DAC/amp to compare with the Flow, but as memory serves Hugo was more transparent and clear, but it's also bigger and twice as expensive as the Flow.