Metrum Onyx versus Metrum Pavane

Unfortunately, I have not heard the Onyx but I have owned the Octave II, Hex, Pavane, Adagio, and finally settled in with the Pavane L3.  After owning the Adagio as well as the original edition and (more recently) the highest level Pavane L3, it is my opinion you cannot go wrong with either.  The Adagio run amp-direct provides a very simple and great sounding alternative.  The Pavane L3 is just as good but only improves on the Adagio in the area of tonal density and only when used with a very high quality preamp.   The Adagio has slightly better resolution  but that is splitting hairs.
I use the Antipodes DX Gen3 with a Roon endpoint, which is currently either the Metrum Ambre or the SOtM triad (three boxes) consisting of SOtM's sPS-200ultra (Roon endpoint), tx-USBultra (USB reclocker), and sPS-500 (power supply for both).  At about 1/3 the price of the SOtM gear, the Ambre sounds arguably just as good although slightly different.  I have not yet decided which endpoint I will keep - they both sound great.  Running I2S directly into my Pavane is a plus and probably the best connection between that and the Ambre, but is not an overwhelming improvement over using AES/EBU from the Ambre to the Pavane L3.  I think it is awesome that Metrum offers a user-installable board to facilitate the I2S connection.
As you move up in the line, IME each successive Metrum upgrade provides more of their signature, natural sound while improving dynamics, tonal qualities, detail, and refinement.  They are a very complete company that manufacturers practical, great-sounding, and high quality products, and they are very easy people to work with.
BTW, speaking of unnaturally expanded soundstaging, that is what I heard when I tried the early Lampizator L4 G4. 

Thanks everyone for answers and suggestions.@soix: I know what I’m asking for seems to invite some tube gear recommendations. However, there are also some other things I care very much for in audio reproduction and I didn’t mention because between the 2 Metrum dacs they were irrelevant. One of them is a very low noise floor / "a black background". I’m using powered studio monitors, often nearfield and in a quiet environment and the hiss is annoying me a lot. Also, I didn’t like the Gungnir’s grey background (or at least this was my perception). So I’m a bit afraid of tubes... On the other hand, I’m more of the "set and forget" kind in this period of my like, I don’t want to think about hunting for new tubes, maybe NOS ones, learn about testing or even matching them etc. So I’d rather stay fully solid state, if possible.
You guys are asking me if I like an exaggerated soundstage. To be honest, I don’t know. But I’ve never had the feeling that the stage is too wide, so maybe the answer is positive. I like the soundstage ("headstage"?) width of my first audiophile headphones (AKG K500 and later on AKG K501) very much. My current source, while much cheaper and indisputably much lower quality that the dacs in discussion (Cambridge D300 CD player), has a wide soundstage too which I also enjoy - wider that the unbalanced outputs of the Schiit dac. I have perceived the very wide soundstage of the Sennheiser HD800 headphones as a great asset, not as being exaggerated.

Jan Garbareck - Pygmy Lullaby - Sax is center focused, percussion starts stage slight left backstage with the hand held tambourine drums (I believe that's the instrument) slight right backstage. Then the percussion comes in at stage right backstage. Sax solo ends with keys, drums kick starting center, backed up by bass. Then sax comes back on with the percussion on both sides .

Desolate mountains 2 - chimes in different tones way left off center, keys in middle, snares behind chimes - very slight, way left, then chimes again (different tones....shifting from left to right, back to left - snares very slight behind chimes way left), sax solo accompanied by louder chimes, snares and brush on snare drums, very deep percussion way back center stage, bass stage right. 

I believe you're talking about the tonal shifts in what we call timbre of the chimes, their frequency and amplitude shifts, as well as at the end the varying pitch differentiation....all very clear on Onyx. Beyond that I can't say....this is my high end setup (I had the $200 vintage Kenwood integrated hooked up before)...very high res full range speakers and high end, low distortion tube integrated.

The headstage on phones is very different from a "you're watching a performance" soundstage provided by speakers, so it'll not be comparable. Plus your monitors and unsure if you're sitting on a desk, will not provide the width and depth I am getting from my setup. I would highly suggest using it (if you decide) with your headphones to compare against your current dac.

Onyx is quite transparent, it accurately portrays the drama in this particular recording which I've not heard before. Once again I commend Metrum on a bargain. 

I’m using powered studio monitors, often nearfield and in a quiet environment and the hiss is annoying me a lot.

Dare I ask what speakers you're using and how much they cost?  I'm fearing a potential gross mismatch here in source vs. speaker and amp expense, but I'll just wait to hear what speakers you're using.  I'll just say that if imaging and sounstaging are high on your wish list, not sure powered studio monitors are the right place to start.  But maybe that's just me. 

Just picked up a Jade DAC/preamp and it sounds amazing for the money.
After putting it in my main system today, I am reevaluating whether I should be using the Adagio rather than my Pavane L3.  Consistent with my earlier comments, they are cut from the same cloth and the sound is close but there is maybe just a touch less body and tonal warmth with the Adagio (compared to the Pavane L3 through my preamp) but the resolution, natural sound, definition, and frequency extension are very good.....and that from the Jade, not the Adagio, which is even better.  The Onix is to the Jade what the Pavane L3 is to the Adagio, fyi.