Metrum Onyx versus Metrum Pavane

I think if I was looking what you're looking for, I might look for a DAC with tubes.  My first choice would be SW1X, which offers an in- home trial period that I think is invaluable.  Given the feedback by owners, this is an outstanding DAC that you're probably unlikely to return.  BTW, if you want another recording with outstanding width, pick up one of these.  A lot of the recording lives 3 to 5 feet outside the speakers.  Don't know if it's a phase trick or not, but it's a really cool recording and great music to boot. 

https://www.discogs.com/Various-15th-Anniversary-Sampler/release/7022235

@don -- And BTW, I agree with @nitewulf that a lot of width has to do with speakers and placement, but also amp and preamp. Unfortunately, IME, it ALL matters. IMHO, any very good DAC will provide this width information. My question is, maybe you're looking for enhanced or maybe even artificial width in audio reproduction? And that's perfectly cool if that's what matters to you. Anyway, I'd echo my previous recommendation to audition a DAC with tubes like the SW1X. You can do so almost risk free, and owners speak very positively of an expansive soundstage. Best of luck.

I have been very busy but I will get back to my impressions on known audiophile tracks as well the tracks you mentioned. One quick note is as a headphone listener your experience of soundstage is different than a primarily speaker listener. Of course it’s extremely easy to place instruments and even follow instruments as they move with the Onyx ( Train Song):
https://www.lifewire.com/stereo-test-tracks-3134905

my issue is more what soix mentioned, do you like exaggerated soundstage width beyond speakers all the time? As most tracks aren’t recorded that way.

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.