A couple people wanted me to post my impressions on the differences in the DACs from the FiiO E10, the HRT Music Streamer II, and the Matrix M-stage's built-in DAC. I put a lot of hours on them over the past few days, and I will try and describe the differences as best as I can.
TL;DR;
$150 $80 $30
HRT Music Streamer II > FiiO E10 > M-Stage DAC
1st) HRT Music Streamer II is the most transparent, with the best soundstaging, articulation, and dynamics.
2nd) E10 gives a more a more polite, laid-back listening experience in comparison to the Streamer II. The E10 has a bigger soundstage then the M-stage with less forward mids and a more open sound.
3rd) The M-Stage DAC is quite decent for the price and will get you up and running. More forward sounding, stronger mids, and smaller soundstage in comparison E10. Detail is on par with E10.
Also, please bear in mind that the differences are more minor in real life then I make them sound in my descriptions below. I'm trying to emphasize (< see what I did there?) and exaggerate the differences to make the subtle more obvious. They are NOT "night-and-day differences" or anything like that. They are more like little things I've picked out after closely A/B/C comparing.
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FYI, for this comparison I'm using a Matrix M-Stage as the amp, and alternating the source between the three DACs. I will be using and referring to the E10 as the base-line/reference DAC here, because that is the one I have used the longest. Not that many people have heard the M-stage DAC anyways, and its not like your going to go out and buy the M-Stage just for it's DAC 
Keep in mind I've been self-diagnosed as a soundstage-whore (you should all do regular self-exams!), and I'm listening with Q701s - which probably amplify the soundstage differences. They may not be as noticeable on less soundstage-centric setups.
Matrix M-stage DAC
For those that don't know, the latest Matrix M-Stage revision can be purchased with an optional USB DAC installed for + $30 USD (purchased from TamAudio). This replaces the 2nd RCA input. The front panel input toggle switch will then cycle between the built-in DAC and the RCA input.
The Matrix M-stage DAC sounds similar and on par with the E10 in several ways. I think the level of detail and transparency is about the same between them. Soundstage separation is decent on both, but their soundstages do differ in size and shape. The E10 has a larger soundstage then the M-stage DAC, which has less depth and width in comparison. The M-stage is more forward sounding in it's soundstage and the depth is a little flatter sounding, whereas the E10 is more laid back and distanced sounding. I think the M-stage may prefer to place more instruments in the center than the E10 (or it's just a side effect of smaller width).
The M-stage DAC has stronger mids than the E10 and they are also more forward (E10 mids sounds slightly more recessed and distanced in comparison - although I don't think they are in general). The slightly stronger mids make it sound like it has a little more midrange body than the E10. Bass is very close, but the M-stage may have slightly more bass impact than the E10. I prefer the E10 overall mainly because the soundstage is bigger sounding.
I think if your looking to get an M-stage and don't need the dual RCA inputs, the USB DAC is definitely worth getting IMO - especially if you don't already have a DAC or need a starter DAC. It fits perfectly in the M-stage's previously empty internal space, and it's nice to convert the M-stage into a dac/amp combo all-in-one box.
I also don't think getting an E10 if you already have the M-stage DAC is a worthwhile upgrade. You'd be better of skipping the E10 and getting a higher end one such as the HRT.
HRT Music Streamer II
First off, the improvements you would assume would pertain to a more expensive DAC apply. The Streamer II has greater transparency and detail then either of the other two DACs. The transparency is more noticeable the better the recording is and less noticeable with a bad recording. The Streamer is faster, tighter, more articulate sounding and has greater dynamics - the E10 sounds a little more compressed in comparison. Streamer II has a little more air. When called upon, the Streamer II is capable of more attack, aggression, and impact than the E10 is, which sounds more smooth and polite. For example, a big/intense orchestral hit sounds more visceral through the Streamer II - you want to turn up the E10 to get the same attack but it won't quite deliver it. The Streamer II engages you more.
Soundstage performance is the main reason I looked at and decided to get the HRT Music streamer II. Luckily it doesn't disappoint, and it does indeed trump the other two DACs in this department. The Streamer II boasts better soundstage width, depth, and height for starters. Separation is also greater and more defined. For example, in electronic genres you often get sections with multiple rapidly panning electronic sweeps, and they are more distinct and individual on the Streamer II, where it sounds a little more blurred together on the E10.
As I mentioned earlier the E10 sounds laid back and somewhat distanced in soundstage presentation. There's a space up close and in front where the E10 doesn't like to place things in the soundstage. For example, if you imagine the soundstage as an orchestra, the E10 doesn't like to place things in the front row (like the viola section). It prefers to place them a little farther back. While the HRT MS II can place things far back, it can also place things up close, giving it more room available for creating depth (It's harder to create depth if you can't place things up close to contrast the things in the distance). The Streamer II has better soundstage placement, and is more three dimensional sounding. It uses the space better to create depth , where E10 pushes everything back a little bit farther in comparison, and as a result sounds a little flatter (depth-wise) than the Streamer II.
Another good way to think of the differences is this: the E10s soundstage is a like a big oval in front of your head, whereas the Streamer II sounds like you lean forward and poke your head inside that oval. The soundstage envelops you more and sounds wrap around more to the side. As a result the Streamer II ends up having more options and spaces available to places instruments, which leads to a more diverse/separated soundstage. The E10 is presented more in front of you, so it has a few less options than the Streamer II for placing those instruments.
Summary
Same as the TL;DR: above ^ 
I'm glad I got the M-stage DAC. Like I said above, its quite nice for the $30 I payed for it and will probably compete well enough with anything in it's price range and probably some other sub < $100 DACs (E10, E7, uDac, etc.) I think if your looking to upgrade over the M-stage DAC you should be looking at the > $100 DACs.
I really like the E10 for its ridiculously small and cute form factor, and it's potent performance (both dac and amp). I won't be selling it just because the HRT is a superior DAC. For less critical/non-"audiophile" listening - where the DAC differences aren't really noticed or appreciated (TV/Movie downloads, internet stuff, etc.) - it is much easier to quickly plug in the E10 than it is to power up the "stage" with the HRT and RCAs. The E10 alone does a great job with all my headphones and gives large slice of the same performance improvements you get from a "desktop" (M-stage/HRT) setup.
The HRT Music Streamer II is a great piece as well. I'm quite enjoying it in my setup, and it gives it that that extra level of performance. I think the HRT Music Streamer II > Matrix M-Stage > Q701 is a killer setup. From what I've gathered on it, its one of the better values in DACs, and hi-fi gear in general. If your looking for DAC in it's price range, I think you would do well to consider it.
Edited by chicolom - 4/9/12 at 1:08am
