The hum/buzz with the W5000, L3000, AD2000 and ES7 bothers me and I'm not using the AT headphones with this amp. The buzz is slighter with the Grado HF-1, SA5000, DT880 and HD650. The K701 exhibits the slightest buzz. There's no buzz with the K1000 connected to the speaker terminals. I tried changing power cords and plugging the MP5 directly to a wall socket, but the buzz was still present.
The headphone port is a 3.5mm socket, so I'm using the Grado 6.3mm to 3.5mm adapter. The volume control has steps.
Using the CEC DA53, which has a fixed output, the headphone port's gain is very high. With most of my headphones, it is already loud before the volume control reaches 4 or 5 clicks up from minimum. With the K701, the first volume step above zero volume only produces sound in the left channel. At the next step up, both the left and right channel are balanced but the volume level is already high for me. It's the same with the HF-1 except the left channel kicks in at two steps above zero volume and it is already loud at the third step.
Using the LavryBlack DA10 in combination with the MP5 results in a much greater range of volume control. I reduced the Lavry's output volume, and the MP5's volume control range is useable now. I'm listening to the HF-1 at the 12 o'clock position with the DA10 at 20.
Note that I don't have much experience with tube headphone amplifiers, and this is my first one. Other than this Dared, I've only heard the Meier Corda EarTube, Cayin HA-1A, and a few other Chinese tube amps.