Here is what the manual says. So given that you want the outputimpedance about 20X lower than the input of the next device perhaps it is pretty high at maybe 1KOhm.
The DAC with volume control should sound audibly cleaner and more direct without any preamp between the DAC and the amp. The preamp, however good, will veil a lot of the DAC’s natural clarity, speed and directness. If you feel you need the preamp nevertheless, use DAC at the full volume or order your DAC without volume module. The load presented by the preamp or amp or simply the next analog component that the DAC sees, should be as high as possible. It is measured in kilo-Ohms and 100Kilo Ohms is a perfect ballpark value. More is VERY rarely seen. 47 K is next common value, and it is great too. 20 K is kind of on a low side, but we can handle that. Lower than 20k is bad news. We must configure the DAC with additional cathode follower buffer stage. The DAC will not be damaged in any way, but at around 10K of load the dynamics of the dac will start to fade away. Having said that - every properly designed amp or preamp keeps the load value above 40k. And if it doesn’t - we simply don’t choose such amp because it was not designed with audiophiles in mind.