Is the DAC2 not a digital preamp? Just a dac?
The DVA Digital Preamplifier is simply a DAC that like many modern DACs has an attenuation/volume control. The new DAC2 is the same and can be used in "digial preamplifier" setups.
Can someone explain why it can be better to use a DAC with digital volume control vs. a dedicated preamp for streaming? I always thought there was information loss or a lack of dimensionality when removing an analog pre. 
Considering that the DAC ICs used in the DAC2 and DVA Digital Preamplifier are both 32-bit devices, you've got around 12 bits you can throw away before you can even start to talk about whether the digital loss of information is audible. That 12-bit margin covers 72dB of attenuation. In practice, the DAC2 gets used at around 24-30dB attenuation (i.e., 4-5 bits), easily within the "you don't need to worry about it" range. Also consider that most of what you listen to will be 16 or 24 bit signals, which offer
zero information in the bottom 16 or 8 bits relative to the 32-bit conversion.
So, you needn't worry about digital loss of resolution in any reasonable situation. What you're mostly left with is the overall linearity of the DAC conversion, i.e., its analog performance at low levels. In both theory and practice, the linearity of the DAC2 and DVA Digital Preamplifier at typical listening attenuation is comparable to analog preamps. So, whether you prefer the sound of a setup with or without an additional analog preamplifier in the chain will most probably be down to whether you want the colorations that are present in the analog preamp.
