To answer the original question, given a single source, the answer is a no-brainer, although highly controversial because in my opinion it is difficult to get right in which case people are finding benefit from adding a preamp to the chain.
The preamp is a non essential component, you need a DAC with an analogue section that is as robust as what you get in a high end preamp. Low impedance, sufficient voltage and current delivery so that it can properly drive the power amp input stage and interconnects.
The analogue volume control is a non essential component, IF the voltage of the DAC's output stage can be set so that it matches the amplifier gain and sensitivity of the loudspeakers so that at full volume the sound is as loud as you are ever going to need. In this case you can make use of digital volume control which is possible inside the DAC chip itself without detrimental affects as you are using small amounts of attenuation to tweak the listening level.
From a poll we did recently we know that 64% of the people here (who actually compared with and without preamps) believe a preamp is essential sonically, however it is highly probable that the DAC's that were used in the formation of these opinions were not up to the task as described earlier.