attenuators volts to micorvolts
If your output impedance specification is reasonably high (say 10 ohms) then JUST using resistors is going to be your best solution. They add little noise and drift. 

For example, you could use a 1M:10 ohm divider, using 0.1% or 0.05% resistors. Or lower accuracy if that meets your (unstated) requirements. 

Added noise due to the resistors will be down around the theoretical minimum of 0.41nV/sqrt(Hz), so over a 10kHz BW only 41nV RMS. 

You do need to take proper care preventing errors due to thermal EMFs if you expect to get high accuracy with only 50uV full scale, but that's a construction detail and outside of the scope of this answer as it applies to any possible method of producing the voltages. In general you would minimize asymmetry, minimize material choices that result in high uV/°C EMFs and keep everything isothermal. 

If you need lower than 5-10 ohms you may have to add amplifiers, but that will greatly increase noise and could add large errors depending on the choice of amplifier. 

As far as 'speed', such a divider will be limited by the DAC output- it would settle in nanoseconds with an ideal step input (microseconds at most)- so your kHz should not really be a worry if the DAC is up to the task. If you were looking at really high speed (above hundreds of kHz) you would frequency-compensate the divider by matching the ratio of 1/capacitances across the resistors.