The Good: Price to quality ratio; K5 allows for docking with FiiO DAPs; Plug and play; aesthetically pleasing; Low output impedance; Three gain settings The Okay: Power output will struggle with some inefficient planars; The Bad: No stated power at 600ohms, but likely not very high based on 150mW at 300ohms Tonal Balance: Mildly warm leaning Listening Set-Up: Musicbee (WASAPI+FLAC) -> E17k/K5 -> Various headphones Cost: K5: $110, E17k: $140 Reviewing Process The FiiO K5 and E17k were sent to me from FiiO as a review unit. I have had the combination plugged into my computer and kept running for the entirety of my time of possession, approximately one month as of now. I have tried a variety of headphones with it with some notable headphones being the Audio Technica AD2000, RHA S500i, ZMF Omni, and Sennheiser HD600. I have the Schiit Magni 2 Uber & Schiit Vali 2 (connected to the Modi 2 Uber) and the Matrix HPA-3u that I’ve done AB testing with to compare. I feel comfortable sharing my opinion on these two products due to my time and experience with them, but I always recommend demoing a product first-hand to form your own opinions. Build Quality The unit is housed in some sort of metal chassis which feels rather lightweight given the size of the unit. The volume potentiometer is large and turns cleanly and smoothly, actually a nice feel to it when turned. All of jacks are secured and offer no issues when used. When the E17k is docked it is seated nicely. Features Despite the USB out, the K5 does not have an integrated DAC, it’s used as a bridge for a docked FiiO product. It does feature RCA line-out and line-in, as well as 3.5mm balanced out. The docking feature is the biggest draw on the K5 in regards to features, this allows for existing FiiO products with a DAC to be docked into the K5. Other DACs can be used, but the major draw is the capability to work seamlessly with existing FiiO products. Power Output & Impedance The power output peaks at 1,700mW at 16 ohms with a published 150mW at 300 ohms with a published output impedance of less than 1 ohm - low enough to have a high damping factor even with low impedance IEMs. I am unable to find output power at 600 ohms, but I’m not very optimistic of it outputting enough power at 600 ohms to be considered for headphones at that impedance. FiiO seems to agree, in the specifications the K5 is specced for 16-300 ohms. The K5 has no issues with low impedance and high sensitivity IEMs like the RHA S500i with no noise floor until volumes that would likely kill the driver if music played through them. The K5 powers the Audio Technica AD2000 without a hitch, though that’s to be expected based on their impedance and sensitivity ratings. The HD600 get close to being maxed out with some recordings, but most users will find plenty of headroom here. The K5 does struggle with the ZMF Omni though, which sit around 55 ohms and between 90-94dB/mW. High-gain is a must for the Omni, and some recordings simply don’t get loud enough with this set-up. Sound Quality In my listening and comparisons I find the K5/E17k combination to have mild warmth without sounding veiled. Slightly smoothed over in details, but very easy to listen to as opposed to the Schiit Magni 2 Uber which I find to be a little bright in comparison. I notice no signs of distortion, nor any added grain. Overall a very nice sounding amplifier for the price when docked with the E17k. Conclusion The K5 is a no brainer amplifier if you’re integrated into FiiO’s ecosystem and don’t have huge power requirements. It’s closest competitor would be the Magni 2 and Modi 2 combination, which offers a stronger maximum power output and less vertical space real estate making it easier to sit beneath a shelf, for instance. I prefer the sound of the K5 with the E17k unit though, it’s not as detailed as the Schiit stack, but it lacks the treble grain that causes fatigue over long-term listening and presents music in a slightly more euphoric manner. The K5 is a wonderful amp if you have a FiiO DAP or portable DAC that can be docked into the K5. If you’re buying a DAC and an amp from scratch then I think that the Schiit stack is a better value due to the added output power making it a little less replaceable if you move onto power hungry planars.