I suspected it might be a stretch to find someone with direct experience changing from one of these amps to the other. There have been some interesting replies just the same, so thanks!
Here is a concise update. My next move was to buy-to-try a secondhand Aegir. Near term, it’s working well enough. TL;DR forum members may exit here. The rest is details.
My setup: Roon -> ultraRendu -> DSD -> Aegir -> 88 dB efficient two-way bookshelf speakers (PSB Synchrony One B) in a 12 x 17 room with my primary listening position about 10-11 feet from the speakers. My typical listening level is 55-65 dB.
My listening material is a mix of electric blues, retro-soul, smaller jazz ensembles, chamber music, folk-Americana-roots, and lesser amounts of classic rock.
To recap: smaller room, not listening to the 1812 Overture or electronica at concert levels. For the way I use the Aegir, I hear the Stereophile Class A rating more than Adcom. I can’t seem to come close to choking it or even making it sound bad.
It’s not future-proofing to be happy with this, but it’s still being happy.
If I eventually step outside the constraints that make this good, the selling prices of secondhand m700’s are likely to be the same or lower. My curiosity to hear the m700’s remains, but I will carry that until I have more of a reason to go further.
If someone else beats me to comparing both, I would still be interested to know more.