OP's question ...
Class D amplification vs tube amplification, which is likely to be more dynamic at lower volume playback?
And here I am thinking that enjoyment relative to lower volume playback is speaker dependent. What do I know?
I don't have any experience with the KEFs Reference 1 Meta. Do they sound to your liking when played low? The one review I read (What HiFi) was addressing their sound when played loud(er).
Even so, none of that prepares us for the scale and authority of the KEFs’ presentation. On the end of our reference system, they sound much larger than they are, delivering the kind of chunky bass more often heard from floorstanding alternatives. Certainly, rivals such as the Bowers & Wilkins 805 D4sound nowhere near as large-scale, muscular or punchy.
I have had tube amps (Prima Luna), Class D (Class D Audio), Class D hybrid (Rogue, Heaven 11) and Class A/B SS (Rega, Adcom) amps in my systems for the last 20 plus years. My systems are not in the same league as your equipment is, that's for the certain. While the Class D amps have performed well, I have been the most engaged by the tube amps. I love my Prima Luna/ Musical Fidelity/ Zu Audio set-up and would be reluctant to replace it. Dynamics are not an issue with tubes. I find I have to up the volume to get the Class D hybrid set-up to sing (Heaven 11, Golden Ear BRX).
Be well,
Rich