I have been a champion of the Marantz 1060 as a headphone amplifier ever since I began experimenting with various headphone and amplifier combinations in 2002. The Marantz 1060 pairs up well with high impedance phones such as the Senn HD-580, 600, 650. The results with low impedance phones will vary, but in my experience the highs will be rolled off with low impedance phones such as Grados.
The sound of the 1060 can be either revealing or harsh, depending on the source program. I prefer to think of the Marantz 1060 as being very revealing of any shortcomings in the source material. Since the power amplifier stage can be used separately from the preamplifier stage, it was easy to mix and match the 1060 with other equipment. By itself, the power amplifier stage does sound more than a bit harsh, however, when coupled to the preamplifier this harshness is well controlled. The sound of the preamplifier stage, especially the moving magnet phono preamp, is very good in all respects.
The model 1070, a later-model Marantz integrated amplifier would on the surface appear to be superior in most respects including power, distortion, low frequency response below 40 Hz. But critical listening to the 1070 with headphones revealed a veiling of the music that was not heard with the 1060. Also, the Marantz 1060 will pass ambient sound information better than any other solid state headphone amplifier I have heard. Normally you need a good tube amplifier to hear the subtle sounds of the recording studio or hall ambience. After an extended period of switching between these two amplifiers I put the 1070 away and kept the 1060 in my headphone listening setup.
The 1060 is not as smooth as a good tube amplifier, but it does not need to warm up to sound its best and it does not generate any noticable amount of heat. If you like to switch between multiple sources, listen to vinyl, and even use tone controls then the Marantz 1060 is worth checking out. To be sure, you can buy a better sounding dedicated headphone amplifier if you are willing to spend at least 2X or 3X the price. I have not kept up with prices on these, but $80-$100 was the going price several years ago. At that price it is a genuine audio bargain.