@OP - I suspect you are looking at preamps at the more affordable end of the market as it's those that tend to have built in DACs.
The majority of high end preamps are analogue only.
Using external DAC with preamp with built-in DAC
I need a new preamp. Most of the new preamps I've looked at do far have built-in DACs. My old one did not and I ran the digital outputs from my CD player into my DAC, then ran the outputs from my DAC into my preamp's CD input and it worked well. It seems like I should be able to do that with newer preamps with built-in DACs too. Will this still work? I like the sound of the DAC I'm using now.