Without knowing what make/models you have been looking at, I would caution you to not confuse an external DAC and/or streamer that also can operate as a preamp (i.e. has a volume control) with a true preamp. Typically their focus is on the digital side and do not sound as nice. An example of this would be a Cambridge Audio CXNxxx series as aposed to a Hegel H120 or PS Audio Stellar Gain Cell, which have an analog preamp section and the DAC is an "addon".
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.