Hi,
The max current that each channel is capable of driving is 550uA. This part is not designed to be capable of driving larger loads. It was designed to drive MEMS mirrors which demanded small currents. The typical plot which you refer to should be similar right across the range, so it can provide 550uA across the full specified range of 1V to Vpp-1V. The sink current is not specified on this part as it was not designed for such an application. The output stage consisting of a DAC and buffer configuration as shown on the datasheet is attached.
Michael Collins
Precision Applications Group.