Hi Elduende 14,
The kind of volume control you are referring to are not "digital" in the way one usually uses that descriptor. They may have a digital readout, but, they work by having a digital logic circuit switch discrete resistors, such as those used in stepped attenuators. Some do use a big integrated circuit as the resistor ladder, but, I believe that the Levinson uses discrete resistors. So, the only inherent potential sonic problems would be the effect of relay contact point (vs. the contact points in a stepped attenuator switch). Even the LED display can be isolated from the actual audio circuits so that it is not a potential source of problem (ML Ref. No. 32 does this).
Perhaps, you were hearing the effect of poor implementation of "digital" volume control, or perhaps it was just a coincidence that stuff you heard with such controls did not sound so good, but I don't think there is an inherent problem with such controls.
The advantages over other forms of pots are considerable, aside from the obvious advantage of convenience. Volume tracking between channels is very precise with stepped attenuators. Also, most of these types of attenuators have a lot more steps than mechanically switched stepped attenuators. I personally hate stepped attenuators with 2db increments because the right volume seems to always be in between. While really small steps (such as the .1db steps in the Levinson) are not needed for volume control, when setting channel balance using mono sources, I can hear changes of .2 to .3 db (image shifts position). Try that with any other kind of attenuator.