The SMSL M6 is a DAC/amp combination, originating from Shenzen, China. I was a bit hesitant about investing in Chinesium, especially given that many of SMSL's products don't receive the rosiest of reviews, but I heard enough good things, and had a tight enough budget that I bit the bullet.
Value: It's a cheap DAC/amp for what it does, at $170 on Amazon. I was particularly interested because I heard reviews comparing it to the Objective and Schiit stacks, which, obviously, are a reasonable bit pricier new; I find the comparison valid, after comparing it to a friend's Magni 2/Modi 2 stack. I prefer the SMSL; the distinction is not large, though.
Build: Sturdy little bugger, I think I could drop it from a balloon at a hundred thousand feet and still stand a chance of recovery. It's made entirely of metal, as you'd expect for a DAC/amp at this price range, and there's no hint of tackiness in its accoutrements. It's got a joystick-style volume control, and a digital readout. The joystick is quite functional, and allows you to switch inputs at will. The readout is nice, displays input information (bitrate etc), but the volume readout is pretty small, about a 9 or 10 pt. font. It's no problem if you have good eyesight.
In/Out: Has coax, optical, and USB input, but only 6.5mm aux out. I'm removing a portion of a star due to the lack of a line out of any sort, as I'd have liked to have the opportunity to use it as a DAC to feed my tube amps. Generally useful enough for a mild hobbyist though, and if you need a line out on top of the lovely amp it already has, chances are you could stand to buy a purpose-built standalone DAC anyway (one well-matched with your other amps).
What you've all been waiting for--SOUND: The SMSL has a very respectable sound quality for the money, and doesn't make many tradeoffs in other departments getting there.
Overall: Fairly neutral, open enough, and detailed for the price. Headphone selection will make a bigger difference to sound coloration, detail, and spaciousness than the amp/DAC, by a longshot; this is a chameleon amp/DAC.
Bass: The bass is fast and realistic, perhaps a bit strong on cans with well-represented bass--e.g. HE400i's--by my tastes. It's not unrealistic, though, not really at all muddy, and has acceptable texture and detail.
Mids: Closer to clinical than warm or overly musical, but in a good way. Portrays vocals in a hair-raising way, with good detail and separation. Not terribly forward, but far from recessed. Relatively linear, by my ear.
Treble: Snappy, very nicely detailed, and not too sibilant. Catches the air of subtle breaths excellently, and realistically renders cymbals.
Soundstage: Decent soundstage, but the NS0-1E+HRT Music Streamer II stack has a bit of an edge here, and the Little Dot I+ (5654W tubes)/HRT combo has a notably wider soundstage. As noted earlier, separation is satisfactory.
Comparisons:
Compared to the HRT MS II with the NS0-1E, the SMSL M6 is more neutral, a bit more forward, and slightly more faithful. The HRT/NS0-1E stack has a bit more texture, especially in the upper mids, really giving guitar a satisfactory buzz, probably due to larger dynamic range and faster transients. This is a matter of preference; I give the NS0-1E/HRT stack the "musicality+analog sound" edge, and the SMSL the "fidelity" edge.
Compared to the HRT MS II with the Little Dot I+ with GE JAN5654W tubes and stock op-amp (will update with AD832ANZ in the next few days), the Little Dot/HRT stack has a slightly crunchier, shinier sound, a bit more warmth, and, again, more texture, especially in the high mids and treble; I suspect this is down to the DAC, and believe i very much like the HRT house sound. The LD I+ outputs a fairly faithful bass, but it's a tad less defined than the M6's. The LD I+ feels more authentic in replicating the harmonics, dynamic range, and transients of instrumentals. The SMSL M6 is clearly the lose here in terms of enjoyability, but wins for tight bass and more clinical presentation, useful for critical listening or studio use.
Headphone compatibility: Works excellently with HE400I's (what doesn't?) and MSR7's. A bit weak on mids for the HP200's, but they work together decently once your ears adjust, or if you prefer a less aggressive mid range. Works decently, for a desktop amp, with LZ-A4's, but can produce a bit of a hiss at high volume settings when nothing is playing. I generally don't used IEMs with my amps, so I can't say much about how the IEM compatibility compares to other amps.
CONCLUSION:
Excellent amp for the money. Neutral enough that, as long as your headphones suit your preferences, the output sound should be quite agreeable. Fairly linear sound, clean presentation, good soundstage, excellent detail for the money, and excellent build quality.
