24-bit/96KHz DirectSound Mode Measurements:

Frequency response (from 40 Hz to 15 kHz) | dB -0.01, -0.59 | Good
Noise level | dB (A) -98.6 | Excellent
Dynamic range | dB (A) 95.1 | Excellent
THD | % 0.054 | Average
THD + Noise | dB (A) -63.7 | Poor
IMD + Noise | % 0.056 | Good
Stereo crosstalk | dB -91.5 | Excellent
IMD at 10 kHz | % 0.082 | Good
General performance | Very good

Here are measurements using XXHighEnd for playback instead of doing playback and recording both through RightMark. 24/96 file was generated in RightMark. Had a difficult time getting levels matched properly on this, so I can't vouch for the accuracy of this one! (Though, I do think XXHighEnd sounds good...preferring it to JRMC so far...)

This was with Engine 3, which is based on WASAPI. I normally listen with Engine 4, which is based on Kernel Streaming, but the option was unavailable due to the measurement setup and configuration.

Frequency response (from 40 Hz to 15 kHz) | dB +0.06, -0.52 | Good
Noise level | dB (A) -102.5 | Excellent
Dynamic range | dB (A) 102.9 | Excellent
THD | % 0.037 | Good
THD + Noise | dB (A) -66.6 | Average
IMD + Noise | % 0.045 | Good
Stereo crosstalk | dB -98.4 | Excellent
IMD at 10 kHz | % 0.253 | Average
General performance | Very good

As to be expected, the NOS treble roll-off is evident in these measurements. At 88.2KHz or above, this becomes much less of an issue (no more than -1dB at 20KHz, with 96KHz sampling). I find it helps me listen more comfortably and develop less fatigue over time. I do prefer a slightly dark sound as-is. The roll-off really isn't that noticeable at 88.2KHz or above, but you can definitely hear it at 44.1 or 48KHz. Setting the hardware to a higher sampling rate and using software upsampling can bring some very noticeable benefits. At that point, you can get into the fun of picking different upsampling methods. I'm currently using XXHighEnd's Arc Prediction method, as that is supposed to have no pre or post ringing.

You'll also notice the weird IMD measurements, though these do almost match the 0.04% distortion as posted on Metrum's website. Based on what I've learned about NOS DACs recently, I had been told to expect issues with harmonic and IM distortion. THD does show spikes at each 1KHz interval but is clean otherwise. THD + Noise was generally rated as average or poor.

IMD really looks interesting, though. I verified it looked this weird on my Auzentech sound card's line-in as well. I don't understand all the science behind this, so I'm not sure if this is typical of NOS DACs, unique to the Metrum implementation, or even how this will necessarily affect the music we listen to. I'm also not sure how to read IMD swept tones measurements nor do I know if they really tell us much. I'll need to do more reading on IMD...

Other than what I've noted, measurements show a lot of good qualities as well. You can see situations where the DAC pushes the limits of the A/DC. It might not be measuring at reference-level quality, but it does well enough for the most part to not leave me worried as long as it sounds good to my ears.

Unfortunately, I'm not at a position where I can give good, meaningful, and trustworthy impressions about DACs or the differences between them. I'd have to hear a lot more gear and do many more listening tests before I would feel comfortable making anything more than a guess.

That said, I can say with the Vali or Leckerton UHA-6S Mk.II and modded Tascam TH-02 (XXHighEnd software), I'm not hearing anything that's off about the sound right away. In fact, during my Vali listening tests, I found the Vali with Tascam did a fantastic job resolving fine, quick details with drums and cymbals (think fast progressive metal, anything that is easily smeared over). It did well outside of drums and cymbals, of course, but I was most struck by that right away. I found it very easy to track and place almost all aspects of what I was hearing. And, yet, I did not notice anything sounding harsh or unnatural (outside of the usual harshness of my go-to bands and genres). Very nice. Also noticed good dynamics, plenty of layering and depth to the sound with nice space between instruments and vocalists. Again, very happy overall so far...had a lot of fun listening and digging into the fine details of the music.

Now, I figure that if the Vali with Tascam was sounding that good, the DAC behind it had to be at least just as capable in order to present that. It might just be a good combo that works well together. I can't say for sure, and my listening tests have been limited to just the Tascam so far with those 2 amps. Take all of this with a grain of salt, but so far I am pleased. I'm also not necessarily saying it's the bestest setup I've heard either, just to make that clear. I'll have to listen more.

If anyone has any ideas on other tests I can and/or should run with my current setup (don't really want to pay money for more hardware or software...), let me know! I believe it was ultrabike that mentioned ARTA to me, so I might try that and REW to see what results they provide. Anything else? Questions? Though ts? Tips?

I would like to figure out ways to test impulse response, sine and square wave response, jitter, etc. Not sure what, if any, additional hardware or software (not free) I'd need for that. I'll look more into what ARTA can do.

Edit: Looks like ARTA might offer this functionality. I'll experiment with it tonight and post my results.