I have been listening to through my Capella for about 20 hours now and find them very transparent indeed. A/B switch-testing between the Capella and the BM II confirms this.

Initially I thought the impact of this HF-amp would be more dramatic but I now hear that its role is much more subtle. What I really enjoy is that I no longer listen to my cans playing music to my ears but I actually experience every musical performance it presents. Classical, jazz, pop and chant are very spacious/3-dimensional and every single instrument and voice is in proportion and not intrusive. Also, the Capella (unlike the BM II) reveals little to none hissing with voices.

I played with various setting of hf/damping/depth but did not (yet) hear any differences with my beyer DT-990 Pro cans (250 ohm). Gain is the only setting that has an impact on what I hear. I followed the manual and turned the volume knob almost to its maximum and tempered the loudness by setting the gain. I guess hf/damping/depth could make/makes a noticable difference when you use headphones that are generally hard to drive but I understand from the manual that these settings are only supposed to take off the edges if necessary.

All-in all I am a happy listener.