Explanation Of Amp Pre Amp Headphone Amp
also why are people calling it a pre-amp and what is the difference between an amp and a pre-amp
pcf already answered this, but I'll put it in different words.
The amplifier is the device that drives the speakers. Its only role is to amplify a small (line-level) audio signal to create a powerful signal that can push speakers in and out.
A pre-amplifier is a device that preceeds the amplifier. The pre-amplifier determines what the amplifier is amplifying. Specifically, it is a source selector and volume controller. In other words, it allows you to choose the source (CD, tuner, computer, phono, etc) that you want to hear and allows you to set the level of the (small) signal being sent to the amplifier. In most cases, amplifiers have fixed gain, so the pre-amp's volume control is the main volume control of that system.
All DAC1's are also pre-amps because they have a source selector (to switch between signals from multiple digital sources) and a volume control. The DAC1 PRE is a more typical 'pre-amp' because it can accept analog sources.
All DAC1's have Benchmark's HPA2 headphone amplifier built in as well.
All DAC1's have a 'DAC' (digital-to-analog converter) built in as well.
Let me know if I can answer any more questions for you.
All the Best,