For those following it, I did
finally try the D5k on the Mullards, and, Lyr's still too noisy for them. I hereby rescind my apology to Rope
It's not
as bad as the GE's were in terms of noise with all kinds of spurring and whining and screeching like sound was "leaking" through tiny cracks while under extreme pressure. But there's a slight background hum, and the whole thing is much more susceptible to noise from the Squeezebox's WiFi transmissions while other headphones don't pick up that noise, and the D5k doesn't pick it up from an SS amp. So I still don't think Lyr and Dxxxx are a good match, though Rope can certainly disagree