As I finally arranged my small headphone corner in the bedroom, I was able to spend some time on listening sessions with the Ultra. No measurements this time.
I've used Mogami 2497 and 2534 cables connected to the Topping A90D amp with Hifiman Sundara cans. My headphones were eq'd according to oratory1990 suggestions on the Ultra, with 87% volume limit for a headroom. And the competitor of the Ultra's internal DAC was Holo Audio Spring 3, connected via the USB cable. The one delivered with the DAC. Output levels were matched. I was listening to the female jazz mainly.
I found the sound coming from the Ultra rich, detailed but not fatiguing. It was definitely a pleasure for me. But I had a feeling that it lacks an intimacy level delivered by the Spring 3, which was able to show some subtleness unreachable for the Ultra. Maybe it's just an imagination, I cannot arrange proper blind tests actually to verify it.
Anyway, the Ultra paired with the Spring 3 is my choice for now and I'm extremely satisfied with results.